Keeping sperm inside...

Weird question but I keep getting different answers... after he cums do you HAVE to hold it inside you for one to stick or as soon as he cums will one stick if it’s going to?? TMI** but my bf cums alotttt and it feels like it leaks more than stays in but as soon as we’re done I have to pee! So it stays in for a couple seconds than I rush to pee.. so I wanna know if that’s lessen my chances to get pregnant.