Sometimes it IS the fireworks and vindictiveness between the parties that causes one to want out of a relationship.
My husband's ex was always screaming at him, hitting him, and throwing shoes at him. She resented his time with anyone but her (he was a young professional getting established in his field, and she was suspicious of every business trip, every late night working, etc. Her whole identity was him and her goal was to get knocked up asap and be a SAHM. She quit work the day she found out she she was pregnant. Geez. They were, frankly a miserable match, and the kids are far better off not being in that contentious environment. Why would anyone want to continue to face that at the end of each day? He's not a different guy now, same guy, except now he has a partner with whom he can communicate.
I met him many years after the divorce, and I do not understand what her problem was, as we get along great. He cooks, cleans, does laundry, makes things for our daughter, fixes stuff, almost never wants to hang out with the boys and always heads home right after work, doesn't drink, do drugs, or care about fancy cars or showey clothes. He's a great husband and a great dad, yet he and ex could not get along at all. WE had a track record of five years knowing each other before we married, and two years of marriage before bringing our daughter into our lives. And his ex has no business resenting our home and what I provide my child. Ex has even more education than I - she is no less capable of providing for her kids than I am of providing for mine. She still gets the same CS even though he can't make near what he did when they were together. Because I maintain our standard of living. She has the option to do the same and is no less able bodied than I- her kids are quite a bit older, actually.