My crazy ex-wife was like that.
She was jealous from the start and used to go ballistic if I ever even so much as spoke to another woman.
She went mental once because she phoned my work and the female receptionist answered. It was of no consolation that the receptionist was not even in the same building, let alone the same room !
She once threw a tv at me because I didn't look away quick enough when a hot woman came on screen.
Believe it or not, she was even jealous of the song "Boys of summer", because she thought I "wanted the sl*t in it more than her !"
Anyway, somewhat ironically, she had an affair or two, and we split up.
She moved on and was with another guy. After a while, I moved on and started dating again.
She saw me with a new date in the car, and really started being hostile.
This lasted a month or two.
Next thing I knew, she was being super nice, and stupidly, I took her back.
She was ok for a while, then the jealousy came back.
Despite her having at least two more affairs, and having two children by different guys and pretending they were mine !
Eventually it got out of control and I left.
One of her affairs moved in with her pretty much straight away.
A year later, same thing, she'd found out through my son that I had a new g/f and really kicked up the hostilities.
She started using my son as a weapon against me, and eventually stopped me from seeing him at all, after she'd got a message that me and my g/f were getting married.
We weren't, we were only attending a friend's wedding.
She never stopped being hostile after that, refusing to divorce, being a ******.
She's been remarried twice since, and still can't handle the fact that I've moved on.
You just can't fix crazy. that's what it boils down to.
These people are devoid of logic.
My theory is that they think if presented with a chance to cheat, they believe everyone will, because that's what they do. That's their world.