Should I pull out if she's on the pill?

My girlfriend is on the pill, and we used to use condoms until she developed a latex allergy. We also hated condoms and started wondering why we were even using them in the first place with her on the pill and such. Anyways, the best part for both of us during sex while using condoms was a shared orgasm. When we stopped using condoms we also decided that I should start pulling out. Well, as you all know, pulling out is not nearly as stimulating for us guys and pretty dull for women. My girlfriend and I are in a serious relationship. We're also teens who are in school, so pregnancy would be very, very undesirable. I'm just wondering how trustworthy the pill is? If I ejaculate inside her every single time we have sex how likely is it to do it's job every single time?