These are good responses, and good advice. Since you say you hardly ever think of her in real life now, it sounds like you are ready to move on. If you were still, in fact, dwelling on her, then that would indicate you need to do some recovery work and healing before attempting a new relationship. This does not seem to be the case with you. It was just an unfortunate coincidence that you saw her at the concert. Good for you for going out!
I know from experience that one must heal before attempting to become involved with another romance. It's unfair to the person you are meeting and trying to get to know, but going out socially and meeting people is a good thing, and sounds like you're ready !
Patty