Ultra serious!!!!! Plz help

[Beaux]

You know? This one really depends on the angle your trying to accomplish. I have (unfortunately) had a couple similar circumstances in the past and I gotta tell ya, it is a die die situation. Your damned if you do and damned if you dont. One way or the other your caught in the crossfire.
Perhaps he is the telling the truth. Idk. but honestly? I doubt it. People who cheat, cheat cause they like to. period.
Imo. At this point, cause he knows that you know, eventually your gonna be in the middle of a big wet mess.
If you tell her now, your gonna be dragged through the whole thing and if she stays with him then you will automatically become the bad guy.
If you dont tell her now then ya better not EVER tell her you knew and pray that she never finds out cause she will be pst at you for NOT telling her.
I feel for ya dude.
Good luck.

[AILU]

I think it really depends on the nature of their relationship. If it was indeed just one isolated incident (he might be stressed out or something that day), and your sister and him are still in a stable relationship (you may try to get some idea by just asking your sister how she feels about their relationship), then probably remaining silent is fine.

The really issue is what is in the best interest of your sister. Would letting her know this affect the relationship that would otherwise go pretty well? Would letting her know this help her realize earlier that their relationship needs some fresh effort? I guess what I'm suggesting is that the best solution requires knowledge of the actual state of their relationship and of the kind of person that your sister is.

[marshlander]

I think it really depends on the nature of their relationship ... I'm suggesting is that the best solution requires knowledge of the actual state of their relationship and of the kind of person that your sister is.

Do we ever know even those closest to us that well?

You may talk to your sister in a hypothetical realm and hear her say she would like to know. That doesn't mean she wants enough details which she could only use to torture herself. At the same time you are in a lose-lose situation. You could see what pressure you could apply to your "best friend" (again, debateable since he has put you in an impossible situation) to explain his once in nine years (really?) error of judgement to her. He's going to have to explain if she ends up with a dose of something nasty anyway. He owes you (his best friend, remember?) that much for putting you in this situation. Once he's dealt with that you might need to have a word with your sister to explain why and how you dealt with this the way you did.

What a mess. Good luck.

[jbrowder24]

Does he go out drinking a lot? If alcohol is a contributor in if he's more likely to cheat, then the amount he goes out drinking should perhaps be considered.... was it a one-off, or does he go out to bars a lot? Some people just can't control themselves under the influence unfortunately

I usually believe in talking things out with friends and giving them a second chance to prove themselves - something that hasn't always been afforded me (I've never cheated but in other situations). The bond with a sibling though... it's definitely tough.