I heard that sperm die the second they hit oxygen. if that's so, how could you get pregnant during dry sex?

Air definitely won't kill sperm in seconds! In fact, when you get a sperm test the lab you ejaculate into an open container and then the technicians let it sit for thirty minutes because it's easier to see moving sperm cells than it would be if they looked right away. (See sperm tests explained here or here.)

Bottom line: wet semen can still contain live sperm outside the body for *at least* half an hour.

Thanks, Tiny.