This is a very one sided way of seeing things. The reason women (or men) might do something similar to what the OP describes is because they were not getting what they needed from their existing relationship. Just because the OP plays the victim here does not mean that his woman was happy with him. We go through phases in our lives, and we need specific things from each phase in order to progress as people. That woman felt she needed a family, and she was not getting that. So she did what she could to get that. Sure, it might not have worked out as she planned about it in the beginning, but at least she went for what she thought it was the right thing to do.

You might argue that "first you divorce, and then you find someone else", but we all know that there are no guarantees in life, and no one wants to risk being alone. Besides, people still love their SO, even when they cheat. It's just that there's something that's just not fulfilled.