WGH, I don't know for sure what happened with husband and the end of OW1 (nor I know how/when it really started). When OW1 was gone I was already back to our home town and my interaction with husband was small. He never told me much about her, and I never asked. I was only ojnce told by a person that it did look like a match made in heaven. My response was "It will not last, also, you've only meets us after he left, so you don't know how we were when we were together not when we started dating".
But, for small clues, I think it was her that finisehd with him. When he left, and for must part of their relashionship, he had is weekend days free. She lived away and could only be with him on the weekend. Given that he had, before she come along, took to DJing, his weekend nights were taken. So, when he left his job and took another one that made him work weekend days, he no longer had any time for her. Most likely she no longer saw the point of being around a man that could not have a moment for her.
He still leads the life he led when OW1 was gone, but OW2, for what I get, likes that partying, DJiing, running around from a place to another like there is no tomorrow (they meet in a club). The little I know about OW1 she was more quiet, mommy type, nice and caring, the sort that wants to rescue the unhappy husband. OW2 is a narcissist, so, she wants to be me, she wants my life. She has created much more problems than OW1.
I think he went after OW2 because, after OW1 a) I was not willing to be his girlfriend and did not want to take part in that crazy life we has leading; b) he had never been alone since he was 17 c) he was (and still is) in deep fog.
Sometimes good things fall apart so better things can fall together. (Marilyn Monroe)