I messed up, HELP ME MOVE ON!

I've always had insecurity and self esteem issues from the time that I was about 13 up until now (I'm 22) and I'm starting to realize/feel as if it is what has ruined or at least helped ruin my past relationships. After the break up of my first love and boyfriend (he cheated on me and concieved 2 kids by 2 different females), I felt the need to be alone, but maybe a couple of months later I met this guy and we became really good friends. At the time we were both talking to other people, but the connection we had felt so real. We wanted the same things out of life and a relationship and shared a lot of the same values. After being really good friends for a while, things naturally progressed into talking (he made me so happy) and after about 5 months we got into a relationship. Everything was going good, we were both happy. We spent lots of time together, going out and talking and would do our best to make the other happy. I thought he could possibly be "the one." He was such a good guy. Anywho, we ran into a minor problem (I told him to "chill out" with constantly asking me for something) and he completely fell back. He stopped coming over to see me as much, we stopped going out on dates as much and our conversations became so forced. I would try and try to "fix" things but it would only result in arguments. To make matters worse, he started talking more and more to females that he was attracted to and who were attracted to him, sometimes even on a flirting level. I don't believe that he was cheating on me, but it definitely made me uncomfortable considering where our relationship stood and it caused more and more arguments. We decided to take a break and when we would talk again after a few days, I was expecting things to be good again, but it always turned into more arguments. I guess I couldn't see his effort, knowing how things used to and could be. After a while he got fed up with it altogether and we ended things for good, but I'm having the hardest time moving on. He has moved on now (to one of the females he was friends with) and I just feel as if I pushed him right into her arms. I'm having the hardest time moving on and continue to text him tons of messages trying to "talk," but instead just make myself look weak. I felt like I did nothing but try to work at our relationship. I tried to please him anyway I could and HE fell back on me and stopped showing the interest he used to show and started talking more to other females, but my actions in the way I handled that (sending lots of texts constantly trying to talk, not giving space) wasn't right either. I think the fear of feeling like I'll never find another relationship is what's making it so hard to let go, as well as feeling as though it was my fault, he really was a good guy. Had I handled things differently, the outcome could've been different. He still texts me sometimes on a friendly level just to see how I'm doing, but I always take it as more than it is and let my emotions get the best of me and start sending him texts again. It's hard to let go of what we had and I'm hurting and I know he's moved on and just considers me nothing more than a friend. How can I let go and move on? I feel like this was all my fault!