What if I tell my coworker's wife about his affairs?
Do you think it's your place to inform her?
I don't know, I just feel I have too.
I don't think that is a good idea to do that. It is wrong to get involved in other people's relationships. You shouldn't get involved because you will get in trouble too.
Nah, it will be fine. I'm doing this because it's wrong to cheat, full stop.
Yes, it's wrong to cheat, but it's worse to self-righteously barrel ahead into people's affairs. You could destroy lives. Sometimes it's best to let people navigate these kinds of issues on their own.