This is crazy. Has anyone had this happen?!

My bf and I decided to use condoms for birth control since he's always gone for work and all that. As soon as he's ready to cum, he pulls out, takes the condom off and goes on my belly. Well, a little leaked down near my lady parts. Now I'm pregnant. That was the one time in the past four months we had sex so it's the only time that I woulda gotten pregnant. I thought sperm died as it hit the air. Craziness!!!