I've read that urination actually helps by cleaning out the urethra after ejaculation, though, stopping some diseases - which some people think might be why men have the urge to pee often after sex. So it may not be as evolutionary crazy as one would think

Same for women...

"In every final scan we could see a big, full bladder, even though most of the women went to the toilet before they went inside the MRI,” explains Pek with comical astonishment. “We think it might be evolution’s way to force women to urinate after sex. Perhaps our ancestors developed this function to avoid urinary tract infections, but that’s only a hypothesis."

https://www.vice.com/en/article/qvgkzw/the-story-of-the-dutc...

wait until you hear about the cloaca

> A cloaca is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts of many vertebrate animals.

> All amphibians, reptiles, birds, and a few mammals have this orifice, from which they excrete both urine and feces.

> Mating through the cloaca is known as cloacal copulation, commonly referred to as cloacal kiss.

> The cloacal region is also often associated with a secretory organ, the cloacal gland, which has been implicated in the scent-marking behavior of some reptiles, marsupials, amphibians, and monotremes.