How do you tell when women are done having sex?

I know for a guy, sex is over once he ejaculates. But when is the sex over for a girl? Because I've always been told in sex ed that the guy is "finished" once he cums & that girls don't always ejaculate during sex. But I never really thought to ask about when a girl is "finished." So when does a guy know the sex has finished for both, if the girl doesn't always "finish off" like guys do? ...

Why is birth control always the woman's responsibility?

I heard about a male birth control pill a few years ago but have not heard anything about it since. Does it even exist? Other than the condom, I feel like it's always the woman's responsibility. I know that the consequences of unprotected sex are heavier for women but I would love it if it wasn't always the woman who had to throw her body out of whack by taking birth control....