Uh, he's a jerk?
In all seriousness, it could be any number of things. He could think you're not really a lesbian. He could think that he might have a shot, for some reason. He could be joking around and not realizing you don't get it.
Either way, you need to shut him down, politely. Tell him it's not going to happen, you're tired of his advances, and he needs to stop. Fair warning: you could be losing a friend.
You could tell HIM…, “Fair warning: you could be losing a friend…., if you keep that $h!T up.”
Seriously, ask him you should be friends with a guy who keeps pressuring you for sex? Make him see if from your eyes.
uh, duh! he's not a friend at all if he's kept on doing all those douche moves on her. He doesn't respect her at all. So dump him in all manner girl. A true friend will not disrespect you in that level.