You had started dating Dean after he broke up with Rory. It was going great. You loved him. So much. You'd give anything for him. He loved you as well. He truly did. More than he thought possible... but... he was still left with unsolved feelings for Rory. He never got the proper closure from her, but he hadn't told you that. He didn't want to lose you. He couldn't.
He eventually proposed to you. Though you were both only 19, you knew you wanted to spend the rest of your life with him, so you said yes. You two got married, and things were going well... or at least that's what you thought. Dean was going to make the worst mistake of his life...
One night, he went over to Rory's house... and those unresolved feelings came to bite him in the ass, when one thing led to another, and he slept with her behind your back...