How To Get Over A Crush With A Girlfriend?

I have a crush on this guy that has a girlfriend. They have been going put for like a year or something. He is my friend but we don't talk all the time. He used to flirt with me alot (while he still had a gf) but then not as much and now he is again (they are still dating) he even stares at me and will just look me in the eyes before he looks away. I've tried to get over him and move on to other guys but I just keep on coming back to him. Right when I think I'm over him he does something so I'm liking him again. I don't know what to do, I don't want to be that girl that steals your boyfriend or anything. What should i do?