Guys: Why would you stand up a girl?

I asked a guy that I’d liked for sometime out to a dance, he says yes right away and we make plans and exchange numbers. Then on the night of the dance he doesn’t show up or answer when I called him to see if he got lost. He said the next day that he forgot but, I see him at least 1–2 times a week and we’d discussed it several times. I don’t think that he could have simply forgotten since I called him the night before to tell him which entrance to use ( I was running the dance and was getting him in for free). I don’t understand why he would do that. Now he says he wants to make up, yet he hasn’t apologized for standing me up. Any ideas as to why he would do that? Should I give him another chance, or just forget him?