I fell in love with a girl who already has a boyfriend?

I met this girl at a bar, we had a one night stand, but we decided to date. Well it turned out we had a lot in common and I fell in love with her hard and fast so we got serious. I gave her everything, and today I found out she already has a boyfriend. I feel so heartbroke and I'm so hurt. I don't know who to turn toI fell in love with a girl who already has a boyfriend?Move on! there's more fish in the sea! if she is going to do this to her boyfriend now then what makes you think she wouldn't do that to you?