withdrawal is not a great method of contraception. It has extremely high failure rates esp depending on whether it's her fertile/very fertile or not-so-fertile time of the cycle. And, yes, in such cases, precum can cause a pregnancy, and sometimes some ejaculate MAY go through as well, before withdrawing. I would suggest relying on a better and more fool proof method of contraception for everyone's peace, for avoiding stds and for preventing an unwanted pregnancy.