I am awful with relationships and I know it is because I'm afraid I will end up alone

I am new to this website and decided to reach out for help. I tend to have 3 month relationships and then leave. From what I am told, I am good looking, funny, compassionate, and fun to be around. I am confident in all parts of my life instead relationships. I constantly question "Why does he want to be with me?" I feel like I am not good enough even though I am told the opposite. When I was growing up a family member emotionally abused me severely leading to the feeling of not being good enough. I know it is irrational, but always leave before I get too emotionally involved. My "so called" friends used to make fun of me all the time because I would be in a new relationship every three months. I feel so alone with this feeling. I don't know why I can't get over this? Now I was diagnosed with a chronic illness and I am afraid to date at all. I don't want to end up alone. Now that I entered my 30's I realize I need some support and advice with this. I have a very successful career and now I want to settle down with the right man. I don't want to have this fear and anxiety anymore! I need to get through this initial relationship anxiety. Does anyone else feel this way? Does anyone have any ideas on how to get through the initial relationship anxiety? Any ideas on how to take my extreme confidence with work and friends, and move it over to my romantic relationships? I know it has a lot to do with the early emotional abuse, but can't get it out of the back of my mind in romantic relationships. I am so tired of being a serial dater and really want to find and settle down with that special man! Thank you ahead of time to anyone who responds :)