with the words of the great stifmeister: pussy's pussy man!
but seriously, once we got to the level that robots are indistinguishable from real humans (because let's face it, uncanny valley is a heck of a thing), who could even tell the difference? while there might be people doing it way before that (not judging, whatever gets your socks off), at that point you could also consider it sex with a kitchen appliance. and as most people know, nothing's worse than a dead lay, so even if you have a 11/10 fuckdoll and you're into dead fish might as well save the several thousands bucks and just buy a bottle of rohypnol - added benefit the pussy's warmed up.
the bigger issue is getting there on a technological level. while there might be some legit interest in robotics from businesses so there's money into it to get finally get an independent robotic unit, who would payroll the development of exact mimics and behavior to get us to bioroid level? doubt there's much industry demand to make your miners or worker drones more lifelike. so that's more a thing for academics, which means if we ever get there it's gonna take a while.
we'll be more lucky with a virtual version, because not only can you cut out the whole hardware aspect and focus on software, you can also piggyback on the general development of getting VR more consumer friendly with the end goal of having deep-dive VR, which has much broader demand and use cases. in addition to that, you don't even have to get the full length in AI to bridge the uncanny valley, imagine a machine-learning v-tuber with more advanced speech synthesizing.
TLDR: we're gonna fuck virtual waifus long before the real version.
if you're legit interested and weren't just musing, check out transhumanism and it's aspects, fucking with technology (literally and figuratively) is only a part of all that.
