I remember seeing a movie some time in most likely the 00's (though I have no idea whether it was new or old at the time) about some sort of alien infestation. The key conceit was that these aliens could somehow either infect and mind control humans or shapeshift into them (don't remember which of those two), but regardless of which of those things it was, it resulted in human-looking-things which acted towards nefarious goals.
They seemed to generally rely on seducing normal humans, pretending to want to have sex with them, only to instead plant their alien offspring into those humans. This would end gruesomely for the seduced people, with copious body horror as various alien-looking stuff would grow from and around their corpse before birthing more aliens. I distinctly remember there being multiple moments where a character was seduced, only to be tricked and killed as part of this. I think one of them involved a guy hiring a prostitute (or maybe two prostitutes?) at some sort of brothel. I don't remember whether the guy or the prostitute(s) were the aliens, though, but one of the involved sides died in the process. I think this particular scene was also at the very end of the movie, implying not all aliens died, after previously the protagonists were shown thinking they eradicated the problem.
I think it was supposed to be a horror movie, but I might be misremembering and it could have been a different genre.