Sorry, this may be long!
I'm friends with a couple, X & Y, they've been together about 5yrs, have 2 young daughters and got married earlier this year - think childhood sweethearts been together since they met at school etc.
Recently they broke up, bit out of the blue, X (man) said he wasn't happy and has moved out, looking for his own place, sorting out money for the girls & bills. Doesn't seem very bothered about it which is surprising since not long ago they seemed happy. Y (woman) is understandably devastated, wants him back, wants to work on things but X doesn't seem very interested in doing so.
Recently I found out that he was a work kissing & hugging one of his female co workers - a 17yr old girl, and they left together at the end of the night. It looks very very likely that they have started at least sleeping together if nothing else. Aibu to be furious with him on Y's behalf? X and the other girl have had a somewhat suspicious relationship for a while now and I strongly suspect that he has cheated on Y with her before they broke up.
I just can't believe he would throw away their marriage and family and break Y's heart just for the opportunity to shag a teenager he works with. I think he thinks the grass is greener on the other side and that it's all exciting and new but once the novelty wears off he will be kicking himself for breaking up his family for a stupid short lived thrill. When I asked him about how he was coping with the break up (before I found this out), he said he didn't feel loved and that he & Y didn't do stuff together anymore. He's complained to me in the past that they didn't have sex enough. So basically he has thrown a strop because he wasn't getting enough attention and decided to devastate his wife and children to be able to fuck the first person who shows an interest.
I really want to message him and ask him what the fuck he's playing at - if you & your wife have problems you try & sort them out not run away & shag someone else! But I won't because he has obviously made up his mind to be a selfish twat and it's not my place to interfere 
My other Aibu is that about a month after he got married me & my bf broke up & he started messaging me asking if I was ok etc. This eventually turned into some fairly strong innuendo and flirting with his asking to come round and so on. When challenged on this he said that X knew about it and it was just a joke. I think that is bullshit and given his recent behaviour I'm wondering if Awbu to tell her about this? I don't want to hurt her any more than she is hurting already but I wonder if she might want to know? I also don't know if I should mention this other girl to her, she is so hoping he will come back to her but it's looking more and more likely that won't happen :(
Feel awful for her and so angry at X! What makes me even more angry is that this girl went to X and Y's wedding too! A mutual friend of ours thinks that I should have no reason to feel angry with the girl as she is single etc and he is the one in the wrong which is true but I feel that she should have left him alone since she knows he is married rather than adding fuel to the fire when they were having difficulties :(