I believe the movie is all about the journey of love. Not about who is right or wrong.
At first it all greeny and shiny, but when it's getting old you get bore and frustrated.
Because people change, desires change, body change.
I believe this is what happened when two different agendas people get together with unplanned future.
It was true Dean has some Alchohol issue, but he wasn't a bad father (knowing the child isn't his) . He tried to be a good husband.(though his romantism ends up in a "sex motel") But somewhere there is a huge need of Cindy left void. She always wanted something more but didn't know what that is.