What’s holding me back?

It’s been 6 years since my last relationship ended badly & I still can’t seem to move on. We met in high school & we were on & off for 4 years. I was his first girlfriend & he was first my serious boyfriend (I’ve dated other guys before but he was different). Besides going on dates, meeting eachother’s families/friends, being intimate, etc. we always talked our issues out & apologize afterwards. But honestly the reason why we kept breaking up was because of my mistreatment of him (belittling him, calling him names, distancing myself from him, walking in & out of his life, etc.) but it was to feel better about my demons/insecurities & his family didn’t like me because of it nor did they want him contacting me but he defied them. The thing is I would break up with him yet I didn’t like to see him with anyone else, he got back with another ex girlfriend of his & went to prom with her. I wanted him back but he would reject me until he finally gave in, then I realized us sneaking around (flirting/*** via text) was wrong & wanted to put a stop to it but he wanted to continue it (I would try to avoid him by not contacting him at all but he was persistent) until his other ex girlfriend broke up with him now that he was leaving for college. He came home for the weekend to visit & ask if I wanted to hang out, which I agreed & which would be the last time we would see eachother (we had sex, made things official again & went out to eat afterwards). Things were back to normal but I realized a long distance relationship wasn’t going to work (we hardly saw eachother) & he would put me in a guilt trip anytime I would try to break it off with him though I still loved him. He would say/do all the right things to convince me to stay & once I fell for it, he started giving off mixed signals despite me asking him to be straightforward until I discovered on *** that he was seeing yet another girl the entire 4 or 5 months we were together again. He was very belligerent & dismissive when I confronted him about at first but he apologized afterwards, he told me that he was moving on with the other girl & that he understood if I didn’t want to be friends, so I told him to never contact me again. It caused me to step out of character (harassing him with insults via social networks & go into a deep depression to the point where I quit my job & was without one for 6 months), spend too much time dwelling/drowning in unwanted thoughts/emotions & tried dating other people but even that didn’t help. The realization that he has truly moved on & having to hear him express that had hurt me to my soul. Although I hate him, I still can’t help but think of him everyday (the time we’ve had together) & wonder how he’s doing today though he wants nothing to do with me nor cares if life is going good or bad for me. I decided to give myself time to properly grieve & embrace being alone, I even got rid of the dating apps because they were becoming emotionally draining. I have grown & matured since then & did learn from my mistakes but I’m still overcome with bitterness, I have been considering getting into therapy/counseling…I want to move on with my life.