I would pointedly suggest to him that he change his password. He'll understand the ramifications of the suggestion and realize what you may/may not have been privy too and that he needs to clean up his act (or not). You know enough now so you wouldn't be blindsided. Let him be himself and do whatever he's going to do. I think you're hurting yourself more by snooping and that's you hurting you? Rule #1, don't hurt yourself!