Kind of surprised by all the anti-Cindy sentiment
First of all I think the reasons the marriage (Cindy and Dean) failed are pretty balanced. I'm not getting the "Cindy's a messed up *bleep*" and "Dean was the sweetest" sentiment. I thought there really wasn't a "bad guy" to blame the entirety of the failed relationship on. This seemed like a story of two people who did love each other and because of a traumatic event (pregnancy-aborted abortion/Dean getting beat up) got swept up in the emotion without completely thinking things through. Two people that met each other at the right time, but weren't the most compatible overall. Obviously Cindy's character needs/craves intimacy and thus needed someone like Dean to go through the pregnancy and escape from Bobby. Dean like-wise was able to feel like the hero and shelter Cindy through the storm.
Cindy was resentful towards Dean (likely because of his lack of ambition and alcoholism). Cindy was probably more prepared to leave the relationship than Dean at the point in the film where the audience picks of up, but what I think ultimately killed their relationship was a lack of communication. Cindy internalized things and let her feelings build up inside instead of openly discussing them. Dean on the other hand seems so insecure and defensive, he is unable to carry any serious discussion without becoming angry or dishing out accusations. In fact the one time a serious discussion was attempted in the movie in a calm manner (when Cindy asks what Dean wants to do with his life), Dean immediately becomes defensive and thus ends any chance of overcoming a problem. As the story goes on, Deans outbursts become more violent and immature, culminating in the office argument. Additionally Dean can't seem to give Cindy space as evident at the end of the film but also in the scene where Cindy wants to tell Dean about the pregnancy but isn't ready (so Dean threatens to jump off the bridge unless she tells them). He feels the need to dictate terms. Dean's attempts to bring romance back into the relationship revolve around "getting drunk and making love" again using alcohol to fix his problems.
Again Cindy also demonstrates poor communication like when she leaves Dean in the hotel, but on the whole these interactions are give and take, with both characters routinely doing things that inflame the situation as opposed to fixing it.
I don't see how you can give Dean a free pass for how poorly he communicates and his outbursts. Yes he loved her, but that doesn't excuse the immature actions he takes at the end of the movie. This isn't to say he is the bad guy. He's just as much the antagonist as he is the victim.