My girlfriend gave birth to a baby that isnt mine!?

This is not a troll question, but when I found out my girlfriend got pregnant, I was surprised. I didn't like wearing condoms and she didn't want to get pregnant so we both decided that she goes on the pill. But because I thought I was the only one doing her at the time I promised her i'd stay with her. I was not going to walk away and leave my baby. I was with her every step of the way into pregnancy. I gave up college and got a job. I drove her to every single doctor appointment, and I even signed up to parenting cles. I was happy that I was brining a child into the world and I had a lot of growing up to do to step up to the mark of being a parent and I did that. Then when the baby was born...the baby was mixed race. I wasted my future, time, money on her and she was banging some black person. I don't know what to do.