How do I let go?

Based off my last question, the answer to my relationship problems is to break it off. We tried multiple times and I’m not receiving the care or love that I want or need. My only issue is that I realize I want better but don’t want to lose someone. I don’t want to see him with another person (at least not soon). I don’t want to see him making someone else happy when he couldn’t do that for me. I feel worthless and not special, I want him to change and be better for me like he promises, so I always reach out and work things out. My therapist says it has something to do with my mother leaving me as a child. It makes me feel insecure and worthless. I just need help moving on and growing. I don’t know where to start or how to make it easier. Just the thought alone gives me anxiety and know this is going to be hard.