I am not an expert by any means and can only go by my own personal experience with my ex. First, he was extremely handsome......all the women sighed when he just walked into a room. He had been married once before he married me. He was not jealous or obsessed with her whatsoever.
Even before we married I knew he was extremely jealous but I was a young woman and at the time was very flattered. When we married he continued to worsen. He had timed how long it would take me to get home from work. (17 minutes doing the speed limit.) If I had to stay late and write a letter for my boss and was late even by 5 minutes he was already sitting on the front porch waiting and I knew it was going to be hell to pay.
He would rage and falsely accuse me of having an affair and I never once wanted another man. Finally after years of violent esculating abuse I left him then divorced him around a year later.
He remarried.......he doesnt give a flying flip what his present wife does or goes.
Go figure. I never figured it out either. All I know is I never gave him one reason to be so obsessively jealous.
IMO