Frisky and Risky

I've been on the pill for several years now not because I was sexual active but because my cycle was so irregular the doctor recommended it. Anyway now that I am sexual active we take precaution. I'm on birth control but we don't use condoms but lately my boyfriend has been asking to cum inside me. I always say no but I have two girlfriends who also don't use condoms but use a different contraceptive. I just want to know what the chances of me getting pregnant are if I take my pill the right way and let him cum every once in awhile ..