If there were only two humans left alive, they would probably hate each other.
No, they wouldn't. If it's necessary, humans are very good at finding common ground and learning to like, or at least tolerate, each other. How do you think arranged marriages work?
In a situation of only two humans being in existence, there'd be no tribalism and no need to compete with each other. Sure, they'd be sick of each other in some ways, but knowing there's no other choice, it would be more like old married couple type annoyance. They'd love each other before too long.
Some of you have a very bleak outlook.