The guy that used to like me now has a girlfriend. When I saw them, I couldn't help but feel hurt.?

Well, what happened that you're not together?You can't feel hurt cause he liked you before maybe it didn't go anywhere I'm not sure why you didn't get together at that point.But he deserves to be happy so you can't blame him the problem lays with the reasoning as to why you didn't get together when he liked you.