Should I ask him to my birthday?

There's this guy I like and it's my birthday soon. There's a group of us going out, they know him too, and I was wondering whether to ask him if he wants to go. The only thing is I don't know whether he likes me or not. He's flirted with me in the past but he never starts a conversation with me when we do talk it's never light hearted always serious. I did compliment him on his trousers the other week and every time we know we're going to meet up he wears them, and yes he does have other pairs. I don't know what to think or do.
Should I ask him to my birthday?
Post Opinion