Man spending lots of time alone with best friend's wife. Aibu to think this odd?

I abstained from voting on this. On the one hand, it does sound like they're probably having an affair. On the other, (a) they might not be - give them the benefit of the doubt and (b) this might just be how they want to do their version of marriage - despite your concerns, it might be best not to embarrass them.

Maybe they are swingers and he don't mind sharing his wife 😂

Blimey, it's not even an inheritance related to you re-reading your post (which wasn't clear). You have absolutely no skin in the game.

"...would affect me if it turns out my suspicions are correct cause frankly he'd want to live at home again with them as he's not the sort of person who wishes to stand on his own two feet."

That clears it up. It's what you perceive as 'your' inheritance which would be hampered by him being there.

You absolutely are the worst sort of nosey person there is. This is absolutely none of your business and nobody can or should back you up in your gossipy 'are they, aren't they?'.

What the hell has any of this got to do with the OP?

What about this best friend's wife in all this ?? Do you think she knows her husband is a cheating b**tard ??

I think he knows, hence being non fussed about it.
From your viewpoint, does the marriage seem to be a "normal/happy" one from the outside? If so I do think it's like an open marriage. For all you know, the husband may have his own side kick.

It's odd, but at the end of the day it sounds like it's consenting adults involved.

I have a friend who previously regularly got involved with a married man she met at work. When she was doing that, I would distance myself. Never judge her or get involved, but create distance because I don't need the mental gymnastics that people involved in affairs go through. She was constantly clutching her phone hoping he would be able to sneak away and call/ text. Wouldn't make plans in case he would at the drop of a hat decide he's sneaking out/ lying to his wife to see her. She justified this by "he's unhappy" After a month of it I couldn't deal with her anymore and stopped making any plans with her. l really don't know how people choose to live like that it's unstable and seems like a constant rollercoaster of emotions.

Reality is, this is all you can do is create distance from the situation to look after your self.

If the grandparents were my family, I wouldn't tell them what's going on, but I'd make sure they were secure and make sure I knew if someone was asking to move in/ for money.

It doesn't sound like any of them are direct relations to you ? In which case I strongly advise you simply create distance because when it all goes to shit you may be seen as meddling and you don't know how the grandparents are going to feel. They may take him in and you can't do anything about it.

Are you Carly Simon, OP? She did once write -

Well you're where you should be all the time
And when you're not, you're with some underworld spy
Or the wife of a close friend

someone I know well and is close to me in such a way that any fallout would affect me. Maybe not directly but definitely indirectly

🙄 it’s cool to like a gossip on Mumsnet, OP. Let’s not pretend it would affect you to the point you need advice over it. Yeah, it seems dodgy on the face of it, but who cares. Stay out of it.

I believe people can have close friends of the opposite sex (although many dont agree with me) however in this case with the history between them and the regularity of their meetings it does sound like an affair.

It's unconfirmed so best stay out of it. Am I right in saying it's in your and GPs best interests that this marriage doesn't end anyway so definitely don't be adding fuel to the fire and encouraging a break up. Affairs don't always end in break ups, the husband might know what's going on, it is possible (but unlikely) that they are not having sex but have a shared interest that the DH doesn't care for and are hanging out like old pals.

Oh what a mess OP. I'm assuming the husband is your brother. They all sound a disgrace.

It's pretty clear there's an affair happening. You can't let your brother back in your parents' house so I'd focus energy there.

I've a similar sibling who I constantly fret is going to put my parent in an early grave.

Not your circus, not your monkeys!

How would it affect you indirectly?

Well if she is cheating on him I guess your cocklodger brother would get half the equity in the house as they’re now married if he divorces her. So he might not move back in with your parents. Maybe that’s his plan.

It's really none of your business. Maybe they have an open marriage. Maybe they're happy with the situation you don't know. Don't get involved and concentrate on your own life.

It seems to suit them all. If the DH didn't like it he'd come home unexpectedly and catch them at it. But instead, he gives them alone time. To repeat - it suits them all. Maybe they're doing crochet, throwing pots or some other hobby together that he has no interest in not really. I would keep out of it. If the marriage breaks up and he wants to live with you/your parents, say no. In the meantime, it's better if the marriage doesn't break up isn't it? So leave them to their little arrangement.

Sounds like he's allowing her to have sex with someone else and if so that's their business really. He knows so there's no reason to concern yourself with it.

Best friend and husband reignited their affair?! Who is sleeping with whom, OP? Make up your mind.