Not even condoms are 100% effective at preventing pregnancy!!
I've gone down on 2 or 3 girls who may have been "looser" than I would've liked. Do I worry about catching HIV? Yes. Do I wear condoms whenever I fcuk? Yes.
I've come to the realization that if you worry about STDs and pregnancy and all the awful sh!t that can happen as a result of sex, there's no way around it. You either get laid and take what precautions you can, or you stay abstinent. Either one is a viable solution.
But if RISK is not an option, then you shouldn't be having sex.