I dont think you should feel like 2nd choice. She got to him first, and he didnt just ditch her for you, so what. I would have done the same as him. Let's say he ditched her for you, found out you suck, and then he had burned a bride with the other girl that might have been the Golden Gate?? I say go out with him...well aside from the whole, don't date co-workers thing. That's just difficult both with good and bad.
"Oh Lord it's hard to be humble, when you're perfect in every way. I can't wait to look in the mirror, cause I get better loking each day. To know me is to love me, I must be a hell of a man. Oh Lord it's hard to be humble, but I'm doing the best that I can." Mac Davis