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AIBU?

Share your dilemmas and get honest opinions from other Mumsnetters.

Brother is having an affair

116 replies

strayingsibling · 23/11/2025 19:45

Met up with my brother for a drink this afternoon, first time in ages. We get on well but live a few hours apart. He was at an event near me last night so we arranged to meet up.

He’s late 40s, I’m a couple of years older. Our parents are dead and we have no other siblings. He dropped the bombshell that he’s seeing a woman he knows from a sport they both do, it’s been going on for almost 6 months. He was with her at the event last night. I knew he was unhappy in his marriage and was actually expecting him to tell me he and SIL were separating, but he says he has no intention of leaving her as it would be too disruptive for my niece, who is 14.

He says SIL is suspicious but he has been lying to her and has denied it when asked. SIL is a nice woman and we get on well. I know they are not right for each other but I feel pretty strongly that she does not deserve being gaslighted like this. I also think that the real reason he’s not being honest is that it’s highly convenient for him to have SIL at home to care for DN while he swans off with his OW.

The OW is 15 years younger than him and he says he knows it won’t last but needs to enjoy life (neither of our parents made it past 60 and this has affected his outlook on life). He’s quite starry- eyed about her.

I feel that it’s highly likely SIL will catch him out.The impact on my niece, knowing her father has been lying to her mother, is going to be devastating when she is already dealing with adolescence. It will probably ruin their relationship forever but he can’t seem to see this. I told him he needs to end his marriage and the affair, accept he’s had his fun and it’s over now and deal with his marriage breakdown like an adult. Maybe that way he can limit damage by never confessing the affair.

He’s my brother and I love him and I want him to be happy. But, honestly, what a twat he’s being. AIBU to feel that there is nothing I can do to make this better? Does anyone have any advice?

OP posts:
99bottlesofkombucha · 24/11/2025 02:59

If you can’t tell sil can you phone message your brother daily and ask if he’s still set to blow up his daughters life? That when it comes out you will tell sil and his daughter exactly what you think of his behaviour and how much you hope his dd never finds a partner like her dad?

CalmShaker · 24/11/2025 03:04

99bottlesofkombucha · 24/11/2025 02:59

If you can’t tell sil can you phone message your brother daily and ask if he’s still set to blow up his daughters life? That when it comes out you will tell sil and his daughter exactly what you think of his behaviour and how much you hope his dd never finds a partner like her dad?

That sounds like a real can of worms op and I wouldn't recommend this, youre going to end up driving your brother away in a minute

Maggiebell · 24/11/2025 04:56

strayingsibling · 23/11/2025 20:01

I do understand what people are saying and I really wish he hadn’t told me. But no way am I going to tell his wife because when push comes to shove he is my only family, we’ve been through a lot together and I do not want to lose him. Oddly he wouldn’t cut me off for speaking my mind but my telling SIL would be a step too far. So I need to find a way to persuade him to do the right thing.

I know how you feel. I have 3 brothers and love them all very much.
I would never say anything because its not my business. I would just say to him to do the right thing, but if he is starry eyed about this OW he is not going to finish with her. He said himself that it won't last. Just keep out of it. It's his life and marriage.

strayingsibling · 24/11/2025 09:32

FairWarning · 24/11/2025 02:35

What's the point in this post, you have no intention of telling your SIL.

For me I would be ex communicating him but then again my SIL's are like family to me, many years under the bridge and the love for my nieces and nephews is incredibly important.

You don't sound so close, so being estranged from your niece and SIL won't be such a biggie.

What a horrid brother, you must be so proud, the fact he so easily confessed to you makes me think he knows you also have strange family values.

Sorry but this post says nothing much of your values, even for all your protestations of it being bad behaviour, it just sounds like you want to gossip.

And what is the point of YOUR post exactly? Ah yes, sorry, I forgot that MN is the perfect outlet for getting a kick out of laying into strangers at all times of the day or night. Some people consider it a challenge to find an angle to abuse the OP no matter what the subject matter. Hope you feel better for having done that.

Life is complicated, families are complicated, people are complicated. Your opinion of my “family values” is meaningless.

OP posts:
user90276865197 · 24/11/2025 09:38

Very unfair of your brother to tell you really, especially as he thinks it won’t last. If affair woman is 15yrs younger, she may want kids etc - would your Db be up for that? Starting again as an old dad?
I’d keep out of it OP, its not your problem to solve…

Swiftie1878 · 24/11/2025 09:43

strayingsibling · 23/11/2025 23:44

Thank you to everyone who has offered advice. Lots of food for thought. I will see how I feel in the morning.

You need to be really stern with him and say that he MUST sort out his marriage break-up, or you will tell his wife about the affair.
He is treating a nice person (the mother of his child!) appallingly, and it must stop.

Luddite26 · 24/11/2025 09:43

I would keep quiet and leave him to get on with it.. I'd deny any knowledge if ever confronted by sil. You aren't close enough to her to get involved.
The way I see it is when you do get involved as a third party sil will but some blame on you for knowing even if you tell her today. It would be I might know you knew. Not believe how long you knew etc.
Just don't text brother about it leave no trail and deny any knowledge if ever asked.

Sartre · 24/11/2025 09:45

Yeah, don’t tell SIL because the messenger is always in the direct firing line. She won’t want to talk to you afterwards either way. Your brother is a dick.

ContinuewithGoogle · 24/11/2025 09:50

I would firmly tell him I don't want to be involved, but I would stay well out of it, and of course wouldn't start telling SIL.

I would also try to put in his head that when it's found out, it's not going to protect his child at all, it will be worst than a separation. He will also take all the blame when really it's a 50/50 split.

There are 2 people in a marriage, it's never 100% fault on one side when the marriage is having problems. It's easy to blame him exclusively, but they are both in it. If they were happy, they wouldn't be that way.

I would stay well out of it because you don't know their private life!

BunnyMcDougall · 24/11/2025 09:58

People knowing that your husband is having an affair behind your back—and not telling you—must be a really horrible position to be in once it all comes to light. I can only imagine the humiliation and the feeling of being the last to know. I would feel like a complete fool, and would also feel very betrayed by everyone. This could go on for years, which will only make it worse.

Findingmypurposeinlife · 24/11/2025 10:02

Ilikewinter · 23/11/2025 19:50

Keep out of it, you've told him your thoughts and it's upto him what he does.

Agree. I haven't spoken to my brother in almost 15 years. Huge fallout. He will always choose them, so if you want to keep your relationship with him, just keep out of it and focus on you.

laughingnow · 24/11/2025 10:14

He’s your brother so you can point out the error of his ways and let him know you don’t want to be part of a conspiracy of silence. He’s being selfish, unkind and delusional but he must know that. Don’t smooth his path to the OW but let him know you value your sibling relationship and his behaviour is risking that too.

reversingdumptruckwithnotyreson · 24/11/2025 10:40

strayingsibling · 24/11/2025 09:32

And what is the point of YOUR post exactly? Ah yes, sorry, I forgot that MN is the perfect outlet for getting a kick out of laying into strangers at all times of the day or night. Some people consider it a challenge to find an angle to abuse the OP no matter what the subject matter. Hope you feel better for having done that.

Life is complicated, families are complicated, people are complicated. Your opinion of my “family values” is meaningless.

To be fair on PP, if other people’s opinions on your values are meaningless then realistically, what’s the point of posting?

Your brother is behaving disgustingly, you’ve been put in a shit position but are okay with keeping it a secret, so it is what it is, there’s not much to add to it.

Fingers crossed his wife takes him to the cleaners, finds someone better and he lives out the rest of his life miserable.

reversingdumptruckwithnotyreson · 24/11/2025 10:42

ContinuewithGoogle · 24/11/2025 09:50

I would firmly tell him I don't want to be involved, but I would stay well out of it, and of course wouldn't start telling SIL.

I would also try to put in his head that when it's found out, it's not going to protect his child at all, it will be worst than a separation. He will also take all the blame when really it's a 50/50 split.

There are 2 people in a marriage, it's never 100% fault on one side when the marriage is having problems. It's easy to blame him exclusively, but they are both in it. If they were happy, they wouldn't be that way.

I would stay well out of it because you don't know their private life!

If one of them is cheating for no reason other than selfishness how on earth is it a 50/50 blame lol

ACynicalDad · 24/11/2025 10:52

I'd reiterate to him that telling you and making you keep it a secret was a really shitty thing to do and that he needs to tell her, or break off the relationship for you.

OneAmberFinch · 24/11/2025 10:58

Tell the OW your brother is riddled with STDs and wait for her to chuck him?

Didimum · 24/11/2025 12:36

strayingsibling · 23/11/2025 20:01

I do understand what people are saying and I really wish he hadn’t told me. But no way am I going to tell his wife because when push comes to shove he is my only family, we’ve been through a lot together and I do not want to lose him. Oddly he wouldn’t cut me off for speaking my mind but my telling SIL would be a step too far. So I need to find a way to persuade him to do the right thing.

Oddly he wouldn’t cut me off for speaking my mind

How very big of him.

strayingsibling · 24/11/2025 12:37

reversingdumptruckwithnotyreson · 24/11/2025 10:40

To be fair on PP, if other people’s opinions on your values are meaningless then realistically, what’s the point of posting?

Your brother is behaving disgustingly, you’ve been put in a shit position but are okay with keeping it a secret, so it is what it is, there’s not much to add to it.

Fingers crossed his wife takes him to the cleaners, finds someone better and he lives out the rest of his life miserable.

I asked for advice, that was the point of posting. I’ve had lots of helpful advice, none of which has required the adviser to express an opinion on my personal “family values” and I can assure you that no decision I make will be influenced by the fact that someone on MN thinks I have questionable ethics, any more than it would influenced by someone telling me they had chips for tea last night.

OP posts:
Cynic17 · 24/11/2025 12:39

The real sadness is that your brother told you, OP, because you can't "un-know" it.
However, this is none of your business, so you need to keep out of it and just be available to listen to either/both of them, without taking sides.

ContinuewithGoogle · 24/11/2025 12:44

reversingdumptruckwithnotyreson · 24/11/2025 10:42

If one of them is cheating for no reason other than selfishness how on earth is it a 50/50 blame lol

but there's never "no reason". He doesn't sound like a serial cheater who shags a different woman every Friday and comes home to have his laundry done.

It's 2 people who are unhappy in the marriage. They are both equally responsible for the marriage being over.

I stand by what I said, he's not protecting his daughter and that's a poor excuse, he should just ask for a divorce. That will blow up in everybody's face, and it will make it look like he's the guilty party.

Flippingnora100 · 24/11/2025 19:52

I think that people having affairs like this get themselves into a kind of frenzy. They are so caught up in the infatuation, the excitement and the indulgence in whatever thing that feels missing in their life that the affair is representing to them, that they often don't want to really think about the very real consequences of their behavior. They get so practiced at compartmentalization that they tend to conveniently forget the very real impact of their actions. You've done the right thing by pointing this out, but he probably doesn't want to hear it. For him, the easiest thing is to carry on compartmentalizing and, "having it both ways." It's almost like an addiction where he knows what he's doing isn't good, but he wants more and he feels powerless to control it, even though he knows objectively that it won't last. He's chasing a high. He's basically enjoying what feels missing from his life, whether it's youth, freedom, excitement and adventure or whatever it is that this affair is representing - without experiencing the terrible loss and heartache that being found out or making the courageous decision to end the marriage would cause. In short, he's being unrealistic, short-sighted and selfish.

I think that all you can do is to keep pointing out that he's doing even more damage to his wife and daughter by handling it this way and not taking the bull by the horns and ending his marriage. I don't think anyone can say you shouldn't be loyal to your bother, but you definitely don't want to be in the role of enabling his behavior.

You could ask him what values does he want to guide his handling of this and how does he think his behavior is lining up with his values?

Tuesdayschild50 · 24/11/2025 22:45

Not your business.

ClareBlue · 24/11/2025 23:51

If you ask 100 people who have been cheated on what was the worst part of it they will nearly all say that they felt complete fools that other people knew and they didn't. The humiliation of others knowing when they didn't seems to be worse than their partner cheating. Most know that their partner is a cheat, or suspect they are, or that there are issues in their relationship and the cheating doesn't come as the biggest surprise. But the lingering sense of betrayal of friends and family not telling them when they knew is nearly always said as the worst thing.
There is no way your sister in law will forgive you or understand your position, and why should she. She will get custody of your neice and it's highly likely she will restrict access. And why wouldn't she. So your loyalty to your shit of a brother is going to have consequences. He's much more likely to forgive you if you tell, than she is if you Dont and it comes out you knew.
This is all on your brother. He shouldn't cheat and shouldn't have told you he is cheating. But he has, and you have a choice to make that will have consequences.

ledmeup · 24/11/2025 23:55

The OP can’t tell the SIL, realistically she could then lose her relationship with both of them.

Just keep pressuring your brother OP but it sounds like the wife suspects anyway so it will all come out soon enough.

BobblyBobbleHat · 25/11/2025 02:46

ledmeup · 24/11/2025 23:55

The OP can’t tell the SIL, realistically she could then lose her relationship with both of them.

Just keep pressuring your brother OP but it sounds like the wife suspects anyway so it will all come out soon enough.

She can and she absolutely should as it will be far better for everyone involved. The trouble is, it isn't the easy path. The easy path is leaving it to go on as is and not to worry about the impact that will have on the niece and sister in law. I feel very sorry for both of them, they will feel so let down by the father and now the aunt. I am very certain that if anyone was in their shoes, they would want to know. He's already done the devastating damage to his family, the only way to lessen that is to make sure they no before it gets worse. I don't know why anyone would be bothered about preserving a relationship with such a pathetic person.

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