I don't have children myself but always assumed that parental love is different than a love for a spouse. I have heard so many people (men and women) say that when they held their newborn in their arms, they felt a love they had never believed possible.
I can only speak to my reasons for divorcing my husband.
A couple of years before we separated he changed. He already golfed and played hockey two nights on the weekends but then started spending most week nights with his coworkers or clients. He worked in the financial industry and they tend to socialize a lot. A non-drinker for many years he tended to come home after business dinners rather than head to the bar. No longer. Now he was coming in at 1:00, 2:00 and sometimes even 3:30 a.m. I was alone most of the time, taking care of all the housework and going to bed alone most nights. If he was home, he was tired and/or hungover and didn't want to do anything. Needless to say, our sex life was almost non-existant.
I tried very hard to impress upon him that our marriage was suffering and he would promise to do better, but he never did. I started golfing a lot more just so we would spend more time with each other. Near the end he told me that I needed to find my own interests so that I wasn't bored and therefore annoyed with him.
Obviously this is highly condensed, but eventually I saw no other recourse although I still loved him (still do really) and very much wanted to stay married to him. He was not being a good partner and had made it clear through his actions that he had no intention of changing the situation. Pushing me further and futher away also, I assume, made it easy for him to begin an affair and complete the detachment from me and our marriage.
I don't know what would have happened if I had stayed in the marriage. I don't believe he would have left, as he was still telling me he loved me, wanted our marriage, etc. but I honestly don't know why.