Correcting past mistakes/actions loop

It's been a couple of months since I ruined a relationship of mine. We were not official, but almost, and that thought keeps me in a loop, taking me back to a very specific moment where things got ruined. My mind keeps trying to fix it with a different scenario each time, as if I can travel to the past. I know that I can't, so it 's useless, but I can't stop it. He's got a girlfriend now, and we are on good terms, but my mind is stuck on our wasted potential. It's like I can't accept that his feelings changed or that things will never be the same. My mind used to look for his flaws because I thought he couldn't be my soulmate if he wasn't perfect in every aspect, leading me to think I wasn't in love with him. But now that I've learned about ROCD, I realize how much I loved him, but it 's too late now. I was scared, and I had intrusive thoughts about our future, like him cheating or us being together forever. I thought it was a nightmare, but I realized it was my dream. Those thoughts affected my way of showing affection because I was anticipating it ending or one of us getting hurt. I didn't give my all because I thought it was useless, or better so I didn’t hurt him. I thought I didn’t deserve him because of me not being fully accepting of him. I thought I would be a bad person if he fell in love. I regret it so badly, but the biggest reason why it ended was that we had a lot of issues with a friend in common who spread rumors about us to make us fight, and it worked, leading us to hurt each other's feelings. That's why I can't stop thinking about it; it was due to other people. My mind keeps repeating the same moment when one of our friends messaged my then-partner to tell him lies or show him proof about messed-up stuff. He never told me about this, just now that he ended things with me and admitted that was the reason things got hard. I keep repeating the moment in my head, like me asking him to block her when the fake rumors were just starting, or my parents talking to this girl's parents and asking her to stop. But these scenarios are endless. I'm walking a lot, creating them in my head. I caught myself speaking alone the dialogues of what I could've said. This is taking time from my career, and I can't focus while studying.