I know that my brother is cheating.
Hi. I would like advice on this matter.
Context, my brother J (33) is separated with his wife, K (32) and have been for a little over a year. They married when they were 21 and 20 due to religious pressures. They didn't have a very healthy relationship (K actually cheated on him before the wedding with a friend of my brother but he forgave her and decided to still get married).
Their relationship was always a bit toxic with both of them always needing to be right and neither would back down until K started getting therapy due to childhood trauma. So I did get to see her changing in real time. But, my brother has always had an arrogance to him which has always affected K and her mental health. He never knew how to handle her emotions especially after her intense therapy sessions.
I love my brother dearly, but I know what kind of man he is. I saw him change over the years into a really proud and arrogant man who is disrespectful to me, our mom, and siblings and I've seen him do it to K. (Although K isn't an angel either)
So a little over a year ago they decided to separate and they ended up breaking a lease they signed 2 weeks previously. To get out of having to pay the $6k fine, K decided to tell the leasing manager she needed to move out due to domestic violence. (She assured us he was never physical with her but apparently she believed he could also claim the same thing about her and it could absolve them both of paying the fine). It obviously did not. My brother had moved out a few days before she did that, and since she claimed it was a DV reason, he was stuck with that fine.
So over the course of the year he paid the fine (and she helped him due to guilt) and they've been on a tumultuous up and down regarding reconciliation. My brother has told me multiple times he doesn't want to get back with her although he has not mentioned it to her.
He has strung K along thinking they'll work it out because she has put him on her insurance and is helping him pay her bills because "that's what a good wife does" (according to her)
Me (29) and K have a good relationship and I genuinely see her as a sister. She has always been there for me when I've needed her and she's genuinely one of my best friends.
My brother last year told me he had met a girl, and he brought her to his birthday celebration at a bar forcing me to meet her. I only said hello and then ignored her existence. He was with that girl for a few months and then they broke up.
He is now dating another woman for the past few months named E. Again, I told him that until he had told K that he doesn't want to stay married, I will not support him bringing women around me. He has now forced me to meet her a few weeks ago at my sister's birthday party and just yesterday at my dad's house. I did not speak to her at my sisters party because my brother knows I don't want to meet E but yesterday I only said hello and kept my distance.
K found out about her due to my cousin posting a video of J and E dancing, and she confronted him about it. He denies ever sleeping with any women (even though it's been around 10).
I feel so fucking horrible knowing about what he's doing and trying to stay loyal to my family even though she's also like family to me.
Now my father told me he's going a few days to Vegas and renting an AirBNB, I asked whose going and of course my brother is going and bringing E.
I cried of guilt because I know how much K is sad about it knowing what my brother is doing and yet I know it all and am too cowardly to confess due to losing my relationship with my brother and losing one with her.
The guilt is really eating me alive. I love my brother and we used to be close due to the childhood trauma we went through together but the man he is now, I can't even be around him for more than an hour without hating how I feel afterwards.
Would it be worth losing my brother and telling his wife what I know so she can finally divorce him or should I keep minding my business even though the guilt is eating me up.
Please, advice and thank you.