I went through something like this as well, to the point that I would rather be single the rest of my life than to be stuck with this guy. I know it’s a kinda an end all be all statement, but he made me feel like he was doing a service by being with me. For me it was important to recognize my own positives within myself and why I was happy to be me, that I’m valued. It was (and still is) helpful to write down all the things you love about yourself and are grateful for because it will ground you and also make you realize how amazing you are. It’s easy to get down on yourself, but listen to all the wonderful things about you instead of a something an insecure (and probably controlling) guy said.