Re: To Tell or Not To Tell
No don't get involved but at the same time do see if you can fix that person a bit. Starting from convincing him to have safe sex to not to have it at all out of his marriage. I know its a hard work but it totally depends on that how much you care about that person.
If you think you can't handle it at all than at least keep reminding him that he is doing absolutely wrong and he needs to stop it. It might sink in one day.