I'm similar to you. My childhood was good with no major problems. However my parents did end up divorcing but I was already 21 and my family was pretty much expecting it. I too thought that my marriage would be fairly easy (or at least not hard). I didn't try very hard because I just didn't think it was necessary. I got comfortable and took it for granted.
My W didn't have a terrible childhood but she wouldn't say that it was good either. She had a lot of responsibility with looking after her brother and sister. Because of it she missed out on some of the freedom that most kids enjoy. Her parents are still together but their marriage isn't good. Her dad is an alcoholic and her mom puts up with it. Her dad didn't pay attention to my W growing up and her mom was controlling. I think my W has probably felt controlled for most of her life. I think this is partially why she's seeking freedom now.
Me:38, Wife:36 M:8 T:13 No kids Bomb:3/10/13 W moved out:3/30/13 Started D paperwork: 10/14/13 D final: 12/30/13 To a future of love and happiness...