Quit the game, fake your own death, burn down the house. You'll be fine after that and it sends a clear message if found out.
Just say it straight. "Sorry, I don't play games to hook up with anyone. I would appreciate it if you would keep our relationship strictly gaming buddies." Ai-chan knows how it feels. In the days of CS, RO and WoW, there have always been guys who asked Ai-chan for Ai-chan's number or skype contact. Ai-chan wasn't interested, so Ai-chan always said, "Ai-chan is actually an old hag. So if you want to hook up with a woman as old as your grandma, ask again." Like, I'm sure many of you here jack off to Siri's voice. But after you found out that Siri is older than your mom, do you still seriously fap off to her?
of course the image of siri as an old hag was removed from the mind and replaced by the smoking hot seductive megan fox
just gunna put it here.... but you do realize there are guys who are into cougars, right? One of my friends is and I got him to point out when he sees an attractive cougar... and they all just look like normal middle-aged women to me <.<;; one man's trash is another man's treasure and all that XD
If he's being persistent after you said no, block him and move on. You already said no, that's all you should need to say. If there's a reason you can't avoid him like he's in your raid group or a guild officer, tell your raid/guild leader why it's making you uncomfortable. They'll try to get him to stop or remove him, and if they don't you deserve a better group of people to play with anyway. If it doesn't work out, block him and move on. If he makes an alt or something to get past your block, then you need to report him to the GMs.