Why do some people get into relationships with very jealous insecure people?

I ran into a old female friend / co worker of mine that we always had a great friendship , no sex or no hooking up with each other whatsoever, we were just work buddies and friends’ and we are still friends’ on social media , I ran into her at the store and I immediately said Hi to her and asked her how she was doing , she had a look of fear on her face and I immediately asked her what’s wrong , not realizing she was with her new boyfriend, I looked at him and said it’s nice to meet you , and put my hand out to shake his , but he completely declined my hand shake , he was looking at me like he wanted to fight me , I immediately said I use to work with your girlfriend. He just nodded his head like he was this bad ass , I was kind of laughing thinking. Dude I would drop you in 2 seconds , but I politely said well it was nice seeing you and walked away. Later that evening she wrote to me and apologized for his behavior, I said it’s fine but why are you dating a guy like that , that is that insecure? She said she doesn’t know and she said she is more Than likely going to leave him over it , I said ummm ok , why aren’t you dumping his ass now? She kept making excuses that he was nice to her and he does this and does that for her. So I said it’s your life and your choice but sorry to see you fell for a controlling insecure guy , I hope it works out well for you. And just shook my head. Why do people get into relationships with people like that? What possesses someone to look past the controlling and insecurities in that person?
Why do some people get into relationships with very jealous insecure people?
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