How can I forget my old girlfriend?

Hello to all of you and thank you for your time in answering the questions here. I have a big problem with my feelings. I have a huge emotional lack, which means I've never moved on with my old girlfriends. My last three girlfriends, two that I loved a little bit, and one with whom I had a long relationship and thought she was my soul mate. As a result, I suffer and often come back to them again and again and again and again... in a never-ending loop. I look needy and pathetic. How can I get better, please? Thank you very much.