My ex was very jealous and insecure and I had to sacrifice a lot of who I was. I am still really affected now about 4 months from the breakup, and he found someone else within 3 weeks. He told me that I was the love of his life and he begged me not to leave, although he wouldn't take the steps I needed him to to help sort out his issues.
He was initially very controlling in a subtle way but then later started criticisizing the way I behaved if it wasn't akin to how he would behave/react. I was treading on eggshells all the time. He often upset me by being sarcastic and blunt. I was expected to put him first and spend all my time with him otherwise he would act hurt and neglected. I actually spent a massive amount of time with him and ended friendships, changed my activities and even listened to different music to make him feel better about his jealousy and insecurity. I drove hundreds of miles every week so that I could work and still see him.
When we broke up he would say I had done nothing wrong and said I was an amazing person. And he loved my quirks. But he also openly blamed me for his actions, saying that 'I made him that way'. I can be enthusiastic and friendly and he didn't like that. I was sensitive to him being mean to me and couldn't let it wash over me. He said that whilst I wasn't maliciously doing anything like cheating (although he clearly had some trust issues) my actions made him jealous and insecure, for example, listening often to an 'attractive' musician or enjoying a hobby with a friend instead of him. Most of it was utterly ridiculous.
Anyway, the point of this is that he may be really happy with his new partner who he found after 3 weeks of us splitting. That really hurt - that he would rather find someone new than work at our relationship given how special he told me I was. And so on. There are three realities from what I can see - either 1. he's moved on too soon and he'll just act the same with her if she ever tries anything like having close male friends, being good at DIY or liking music by 'attractive' singers. i.e. he won't change and it's just a plaster. Or 2. she's just different - she doens't react the same, she doens't pander to his jealousy, she's not bothered by his snidey comments, or she doesn't do anything to rile his jealousy.
Or 3. he doesn't care about her in the same way. He told me that his ex had close male friends and even cheated on him. She fancied celebrities and she spent time with friends independently of him.But he wasn't really bothered because he didn't really care about her the same way. He wasn't as jealous for her attention or as insecure about things she liked that he didn't have.
I kinda hope that it's the 3rd, because I thought we had something very special. I am very sad that he couldn't work on his issues. I am very hurt that he replaced me so quickly and I'm confused by that. I hope it's not the 2nd, because that makes me feel like a complete failure.
What I can guarantee is that after all of his whole week of 'soul searching' and three counselling sessions, the deep rooted jealousy and insecurity isn't fixed. It just isn't happening with her.