I had a horrible chat with a guy two years ago, turned out he's a total freak and dirtyminded on the inside. I don't want this chat to exist at all, because turns out he still checks it regularly. Is there some way to erase this horrible thing? Please help
Erase, probably not. If he hasn't published it anywhere, you don't have much influence. How have you come to learn he checks it? Did you not block him? Any illicit material involved?
You're neither the first nor the last to be misled by someone. Best to try to come to terms with that.