[Backstory from another thread to keep this focused, tl;dr near the bottom of linked post](https://np.reddit.com/r/survivinginfidelity/comments/a7ne4x/advice_just_found_out_that_my_mother_53_devoid_of/)

I was originally going to try to anonymously inform the guy's wife and let it resolve on its own, but as time has gone on I've started to feel resentment towards my mother for putting me in a situation where I have to choose which parent's trust to violate. Plus on some level I feel like I need to stand up to my mother and support the man who has put up with her bullshit for the past twenty years.

On one hand I think informing him is the objectively right thing to do, in a void where my parents are identical mannequins and don't have a daughter, but of course that's not the fucking case. On the other hand my step-father has temper issues that might result in physical and/or verbal abuse to those around him, who would be my mother and possibly also my sister. I'm going to be out of town, spending Christmas with my partner's family, so there's also an element of potential assholery due to me making that phone call from a safe distance while my little sister has to deal with the fallout. It's really just the most unfortunate timing, and I'm not sure if it's worse to do this before or after Christmas. I might inform my brothers, who will be much closer, so that they can rescue my sister if need be.

Also sorry if this is completely the wrong subreddit for this kind of question. I'd appreciate suggestions for other places to ask, if any of you have any, aside from the one from the linked backstory.