He's asking me out but I know he has a girlfriend, what do I do?

[I ♥ Pancakes]

This guy I met through mutual friends asked me to facebook him. I added him and he sent me a message saying do.you want to go out tonight i really like you. We can get a bite to eat. The thing is on his profile it says in a relationship and i noticed he had a picture of a girl on his phone background. He said ignore the thing on facebook im not a wanker but I dont know why he would ask me out if hes in a relationship. I went out on a date with one guy who told me he was seeing another girl...i dont want that to happen again. I don't want him using me to get back at his girlfriend since his relationship with her is on the rocks.

What do I do? Should I go out with him? I don't want to be someone's rebound thats all