Warming up will just lead to warming up longer. then longer. Yes, all cum has sperm, so the chance of pregnancy is there. And honestly, the chance of pregnancy of a few in/outs is small, but you don't want to be the unlucky one. There are ways to reduce the probability of pregnancy: female contraception pill/foams, avoiding ovulation, and descreasing the number of unprotected sexual encounters.

I feel for you guys, condoms suck ass, and abstaining from sex isn't real. Good Luck.