Sex and Pregnancy.

To clarify, I'm a male. My girlfriend and I are getting closer and closer to having sex. We just grind quite a bit, but nothing more. Both she and I don't want kids, now, and probably ever. We already had that talk. But I've heard of cases where condoms and birth control pills together still give way to pregnancy....This makes me so nervous to even go inside, and I can't bear the thought of having kids...our future careers are not fit for parents, and we would not be happy at all settling. So what can I/we do to alleviate these fears?