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AIBU?

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Original poster

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:
BobblyBobbleHat · 23/11/2025 19:49

Ugh, he sounds really dreadful. Brother or not I'd be telling my sister in law everything and letting her make the choice as to whether she wants to stay with someone that treats her like that. What a fabulous example for a father to set to his daughter. Id also ask him how he'd feel if someone treated his daughter like that in future. It may help him get some perspective. Honestly, if he wants to leave then fine, but do that first before treating your wife and the mother of your child like rubbish.

Ilikewinter · 23/11/2025 19:50

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

MsSmartShoes · 23/11/2025 19:50

I think that it is kinder for everyone to know the truth in this situation. Let everyone know the facts and choose for themselves.

thepariscrimefiles · 23/11/2025 19:51

It was very unfair of your brother to tell you about his affair if he intends to keep it secret as this makes you complicit in his deceit.

He isn't staying for his daughter. He just wants to have his cake and eat it while deceiving and lying to his wife every day.

It would make me lose all respect for him.

IndigoIsMyFavouriteColour · 23/11/2025 19:51

I would keep my brothers confidence but make it clear how shitty I found it.

Sleepyandtiredandlazy · 23/11/2025 19:51

Personally I would be cutting off contact with my brother because I couldn't be party to his lies and deceit.

Ideally I would tell my SiL what was going on but if that is a step too far I certainly wouldn't be involved in being his accomplice , which by telling you, he is trying to make you.

Bimblebombles · 23/11/2025 19:52

I wouldn’t tell the SIL but would have another talk with your brother soon and explain that you will if he doesn’t.

BobblyBobbleHat · 23/11/2025 19:53

IndigoIsMyFavouriteColour · 23/11/2025 19:51

I would keep my brothers confidence but make it clear how shitty I found it.

I really dont understand this view, just because he is her brother does not mean he can treat people so badly and expect to get away with it. It just isn't on.

MoralTriageJay · 23/11/2025 19:54

BobblyBobbleHat · 23/11/2025 19:49

Ugh, he sounds really dreadful. Brother or not I'd be telling my sister in law everything and letting her make the choice as to whether she wants to stay with someone that treats her like that. What a fabulous example for a father to set to his daughter. Id also ask him how he'd feel if someone treated his daughter like that in future. It may help him get some perspective. Honestly, if he wants to leave then fine, but do that first before treating your wife and the mother of your child like rubbish.

Telling men “how would you feel if that was your daughter (or any other family member that is a woman)” really doesn’t do what you think it does. They don’t care.

Lavender14 · 23/11/2025 19:57

Normally I feel strongly that you should tell the partner who's being cheated on, but I think given that you're each others only family I do think it complicates things.

I think I'd feel a level of responsibility for convincing him to either end the marriage or disclose the affair. I would also be calling him out very clearly on the fact he's using sil for childcare while he cheats, is putting her mental and physical wellbeing at risk and he's setting a very shit blue print for his dd in terms of what a good man is and how they act.

I think he's put you in a shit situation as well by telling you, especially in the run up to Christmas when you'll have to see sil most likely.

I'd tell him that he needs to come clean and give him a timeframe to do it in - I'd probably give him until end of January and then I'd tell her. That's enough time for them to get Xmas over them.

Original poster
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.

OP posts:
LondonLady1980 · 23/11/2025 20:02

How close are you to SIL?
Do you have a relationship with her?

Does you knowing about this affair mean you’re going to have to lie to her in order to protect your brother?

I once kept my sister’s confidence when I knew she’d cheated on my BIL, but that’s only because I knew it had been a one-off event and not a full blown affair. Your brother asking you to be involved in all this deceit and not say anything is a big ask if you get on well with his wife.

Sunnydaystoday · 23/11/2025 20:03

thepariscrimefiles · 23/11/2025 19:51

It was very unfair of your brother to tell you about his affair if he intends to keep it secret as this makes you complicit in his deceit.

He isn't staying for his daughter. He just wants to have his cake and eat it while deceiving and lying to his wife every day.

It would make me lose all respect for him.

This.
What a selfish loser.
He is morally bankrupt and I wouldn't forget that.
This is him 100% suiting himself.

Comedycook · 23/11/2025 20:04

You're totally right not to tell your sil op....it's shitty behaviour but of course your loyalty is to your sibling. All you can do is give sensible advice and hope he listens.

BobblyBobbleHat · 23/11/2025 20:05

What about loyalty to your niece? I'm afraid I think if you go along with this then you will likely lose her. That said, maybe neither your niece or sil need the two of you if you are willing to do this to them. I think it is appalling.

Original poster
strayingsibling · 23/11/2025 20:06

Also I do feel that if I tell SIL her finding out that way could have a worse effect on DN than even if SIL works it out for herself, which she will.

OP posts:
wildone345 · 23/11/2025 20:07

if this was a sister telling a sister would you really tell the brother in law? Doubt it. Why is it different when it’s a brother and a sister relationship?

SouthLondonMum22 · 23/11/2025 20:08

What an arsehole. I'd tell him that he can tell her or you will because now he's making you complicit in his lies and I absolutely wouldn't stand for that.

Where was his loyalty and care to you when he opened his mouth and put you in this position? Selfish. He wouldn't have my loyalty, brother or not.

BobblyBobbleHat · 23/11/2025 20:09

wildone345 · 23/11/2025 20:07

if this was a sister telling a sister would you really tell the brother in law? Doubt it. Why is it different when it’s a brother and a sister relationship?

I would. I wouldn't let my niece find out her father and her aunt have betrayed her. Nobody seems to have any morals any more.

reversingdumptruckwithnotyreson · 23/11/2025 20:09

He’s fucking disgusting.

Your niece is your family too and she has this narcissistic twat of a father and now also an aunt that’s covering for him. He was bold enough to bring his affair partner around you and he feels no remorse in what he’s doing.

I’m sorry but I’d sure as fuck tell his wife, if nothing else so that you’re not complicit in this disgusting lie. Then she can do whatever she wants with that information.

Original poster
strayingsibling · 23/11/2025 20:10

I don’t see SIL often any more as they tend to spend more family time with her parents, while I hang out with my own in laws at Christmas. It happened that way because his and my kids have grandparents on the other parent’s side, IYSWIM. I mostly chat to my brother on the phone or we might meet up just me and him a couple of times a year. I don’t know my DN too well, to be honest, but I remember being 14 and how hard it is.

OP posts:
grumpygrape · 23/11/2025 20:11

thepariscrimefiles · 23/11/2025 19:51

It was very unfair of your brother to tell you about his affair if he intends to keep it secret as this makes you complicit in his deceit.

He isn't staying for his daughter. He just wants to have his cake and eat it while deceiving and lying to his wife every day.

It would make me lose all respect for him.

This is exactly what I was going to say
How bloody selfish to tell you his 'secret'.

ShesTheAlbatross · 23/11/2025 20:11

I don’t know if I’d tell SIL, but I’d make it clear I wanted nothing to do with it, and I absolutely would not outright lie to SIL. So if she asked (he’s said she’s suspicious), or if he ever used me as an alibi and she asked about that, I’d say the truth.

InterestedDad37 · 23/11/2025 20:11

Tell your brother you're not going to lie if SiL asks you about it. He's been very, very unfair to you making you party to knowledge which could also affect your relationship with SiL and niece.

In fact he's been very unfair to everyone concerned. He needs to do the right thing, and quickly too.

ShesTheAlbatross · 23/11/2025 20:14

wildone345 · 23/11/2025 20:07

if this was a sister telling a sister would you really tell the brother in law? Doubt it. Why is it different when it’s a brother and a sister relationship?

My answer would be the same. I might not tell the spouse but I certainly wouldn’t outright lie.