We do know that Pip did have some feelings for Hilary and was pretty broken up after their break up. Whatever his reasons for those feelings (be they purely physical or have a significant emotional element too), it's not outside of the realm of possibility that he was hoping for a chance the two could get back together.
Of course, that's not going to happen thanks to her psychopathy, but, for millennia, people in real life have been deluding themselves as Pip has.