I don't want my gf moving in with some guy who is obsessed with her.
Why do you think she shouldn't move in with him?
I can't trust him, I find him weird.
I agree that it would be a bad idea for your girlfriend do move in with someone who is obsessed with her; that should like a very bad idea. But you need to lay out you concerns to her clearly and rationally, otherwise she might just think you're jealous.
But I am jealous. I am afraid he might be violent towards me.
I think you better talk to her immediately then, you cant let her move in with a guy who might be dangerous. If she still needs to get a roommate do you think you might be ready for a bigger commitment and have her move in with you?