Just because you treated him poorly this summer doesn't mean he gets to act like a child and give you payback. Apologize and make changes in your behavior so that you can with integrity ask him to do the same. If you were sick with undiagnosed bipolar over the summer, you were probably a pain but you couldn't help it. Similarly, if he's depressed now, he probably can only control his behavior so much. That's why you're going to have to put limits on exposing yourself to it. He will make you have some kind of relapse from all this stress. It sounds like you two will need counseling for him to let go of his resentment about the summer. But letting him treat you the same now isn't going to solve anything.
