Half The Time

Ok. I know im going to get a lot of comments telling me how dumb this is but im putting it out there anyway in hopes to find a piece of mind. My bf and I have been using condoms as our main form of birth control but the majority of the time not right off the bat and Valentines Day was no exception. We went for HOURS and after he stopped ejaculating (into the condom or my mouth) with his orgasims we went a little after with the condom off because the ribbing on them was driving me nuts and nothing was coming out so we figured fuck it whats the harm? Wasnt until after the fact that I realised it was during my furtle window. I guess my question is how likely are you to get pregnant from just precum if any at all.