As a parent I can see that a lot of conflict with children has to do with them being (or us seeing them as) something we have to steer and prod in the right direction. And a lot of resent (also reward) is created by having them in your space constantly messing things up or putting demands on your life. When your kids are taking care of themselves, and living as autonomous adults... the relationship changes.

As an adult, I moved back in with my parents for a few months in university, prior to moving out to Toronto. At first it was fine but within a few months the same old conflict with my father came back. Being in 'his' space made it hard to be friends.