that's literally the most instinctual thing ever, they literally fell in love based on sex it doesn't get any more animalistic than that (not a bad thing) they forgo each others superficial traits like personality or virtues(in the beginning) and based their love on literal body compatibility, gotta wonder thats probably how humans mated and paired off with one another because simians also have a some a what monogamous behaviour (birds too), lmao i dont know where im going with this but shit man thats kinda deep in its own way ngl.