If he ain't a bro, then why bother?
Male code of honour of not, it's up to you what you want to do.
No need to involve yourself further IMO.
Because it’s morally right.
This isn’t a drunken one night stand. I wouldn’t bother for that. Genuinely, people make mistakes.
This is clearly an example of one partner being polygamous while lying to the other, over a long period of time with multiple partners.
If OP doesn’t do the right thing, this kind of thing carries on. If he reports her, she may take a look at how she’s conducting herself. She will at the very least, endure the consequences of her behaviour.
OP may be able to save a guy from being humiliated, being a cuckold and wasting his time and resources on someone who is abusing them.
I think it’s entirely the right thing to do.
Sure if she was one fling, who then said she couldn’t see him because she had a BF, we’ve all done this at some point.
This girl deserves commupance.
OP doesn’t even have to tell the dude he was the one smashing her. He could just explain what he knows about the other guys and leave it at that