Definition: Given a real-life anecdote of a complex ethical situation, generate a suitable title that describes the main event/root cause of the situation. Imagine that the given text is a social media post, and you have to write the title of the post, so the users can decide to read the main text or not.
Input: Need some brutal honesty about what I consider to be a morally grey area. 

My boyfriend is really good friends with John (26m), and has been for years. They've been roommates for a long time, during which time John started dating Jane (25f). They became pretty serious and Jane moved in with them about two years ago. I also moved in about a year later and have lived there since. Long story short, the four of us all live in the same house and usually get along. 

I became friends with both John and Jane, but wouldn't consider us close. Jane likes to party a lot, loves attention, and always has her friends over -- this is her first time living away from her parents and it shows. John, on the other hand, is super mellow and easy-going. He’d rather spend all his free time smoking, playing Runescape and mostly keeping to himself, but he’s become pretty tight-knit with Jane’s group of friends lately. 

It’s a relationship, so obviously there’s more nuance than that and they work surprisingly well together. I honestly thought everything was fine up until last weekend. Jane and I end up in the bathroom together, drunkenly chatting about exes for some reason when she started randomly crying about how she cheated. I assumed she was referring to something that happened in the past – she apparently hooked up with an ex while she was seeing John. This was a couple years ago, and I was under the assumption that John had already forgiven her for it and that they moved on, but she started crying that “it’s not just in my past, but it’s my present, too”. I didn’t get any details because I didn’t want any, but she was so upset and begged me not to tell anyone, especially John, because she hadn’t figured things out yet.

I wish she didn’t tell me, and I don’t even know why she did. I ended up deciding to tell my bf because he and John are such good friends, but of course now that just puts my bf in the same shitty situation that I’m in. My bf wants to tell John, but we also know that John is so anti-confrontational, that a) he might not even believe us and b) even if he did, there’s a pretty massive chance that he would forgive Jane again. In either case, we look like the complete assholes and I guarantee that the living situation would crumble into something miserable for all of us. 

So, reddit: do we keep the peace and hope that the cheating makes itself known organically, or do we risk making the living situation hell by trying to be a good friend to John? I’m torn between minding my own damn business and letting them do them, or informing John before they get even more serious. 

For clarity, my boyfriend and I are both 27 and are saving up to move out, but that looks like it’s going to be a ways away.
TL;DR – my bf’s close friend John is being cheated on by his long-term girlfriend Jane. I’m afraid to say anything because the four of us live together. WIBTA if I told John?

telling my roommate that his long-term gf is cheating on him