I was objectively an asshole in my last relationship, how do I fix myself so I never do the shit I did again?

I was an asshole. I really wasn’t ready for a relationship, but because of undiagnosed mental issues I was obsessed with her. Literally obsessed. I couldn’t break up with her, but I used her manipulated her etc. for so long, without even really realizing that’s what I was doing. I realize now I never loved her, there was no respect though. It truly was the biggest mistake of my entire life. She ended up cheating on me which like honestly. Good for her. She’s with the guy and last I knew, really happy with him. Which is good.

I don’t want to do this to another person. I think maybe I should just spend the rest of my life alone. But that breaks my heart. Any advice is really welcome.