I was just wondering the same thing about my H. He has always had a thing about being controlled. I was not controlling. Many of his friends were envious because I didn't put restrictions on him. I only asked that he spend as much time with me (us after the children came) as he did with friends.
When he left, he said the same that he just didn't want to be married any more. That he may have never been meant to be married and that he didn't want to answer to anyone.
Now OW doesn't even allow him to speak to me or have any interactions with me at all. I know this because he spoke really friendly to me in front of her and they left my S17's track meet without H seeing S run and has not spoken to me in person, on the phone, or by email since.
Really strange.
Everything happens for a reason, maybe Dad needs to find that it isn't better out there, he needs to realize how good he had it here. Maybe he will find God and that is the most important thing when he finds Him he will know he is supposed to come home.