Their relationship: Dean is a sweet, genuine, and loyal boyfriend — and he's nuts about Rory. Unfortunately, there isn't much to him beyond that, and after a while they start to grow apart. The problems are only exacerbated by the fact that Rory develops a serious thing for Jess. Their breakup in season three is painful and dramatic, but it seems inevitable.
Why he's important: You never forget your first love, and Dean will always be the perfect example of the perfect first boyfriend. Dean also teaches Rory that simply wanting a relationship to work because it sounds nice doesn't mean it will. Sleeping with him at the end of season four while he is married is a HUGE no-no. And even though Dean ends his marriage and tries to make it work with Rory again, it just isn't meant to be.