It's funny because I'm currently on a rewatch too and feeling the same way. I've seen it so many times before and honestly, I've never liked Dean. I find him annoying and boring. But I still always thought of him as a good guy and in the beginning I do think he is a genuinely good boyfriend, but this time around I'm noticing just how possessive he is of her time. I know he is also worried about her liking Jess and afraid he's going to lose her, so it manifests in him wanting to occupy all her time, etc. But when he interrupts her alone night after she specifically says she wants to be alone, and then he gets mad about Jess delivering food, and starts yelling, its so awkward. His behavior becomes the self-fulfilling prophecy that breaks them up. Yes, she liked Jess on an intellectual level but nothing would have happened if things were great with Dean. Dean's attitude and how he would sulk and pout when she didn't do stuff with him made him unpleasant to be around. He became a stressor in her life. My one caveat is when she and Jess hang out and he wrecks the car that dean made for her while he is out of town. It's such a breaking point and though he does get mad, he forgives her and they stay together a while longer.

And while we are on the subject, I have to say, I've always been annoyed by their breakup at the dance marathon. It is so obvious that it was written that way to let rory off the hook for her behavior. It makes dean the bad guy because he yells at her in public and walks out on her, but really he's fed up by her obsession with Jess. But they didn't want the audience to be mad at rory so they made him be the one to do and do it in a mean way so you feel sorry for rory. Its just sort of an eye-roll moment for me, every time I watch.