Allie was always the relationship type. Dean was more into hookups and flirting. It was supposed to be just a casual distraction after her breakup. Somehow, Dean ended up the one with a broken heart. Spoilers for the season one finale. Dean thought he'd be okay with Allie being with someone else... until it actually happened and he realized he was absolutely not okay with it. Too bad it happens right after he finally tells her how he feels.