How do I stop caring about him?

My ex (M20) and I (F21) broke up a week ago, and I think I’m doing better than expected. I caught him cheating again—not physically, but it still involved flirting, even though he denied it. He cheated on me three times, and I forgave him because it was only online (I know that was naïve of me). He ended things and was so cold about it, as if he wouldn’t have broken up with me if I hadn’t caught him cheating again. He said he wants to focus on himself and his studies.

But yesterday, while I was cleaning my laptop and deleting photos of us and any possible accounts logged in, I saw he was already talking to or flirting with a new girl. A couple of days ago, I also noticed his following count going up. I logged out immediately because I don’t want to ruin my mental health any further.

I once thought this guy was going to be my future husband. He was my first boyfriend, and I loved him deeply. I was his only friend and the person he confided in about his problems. I realized that I don't want to marry someone like him and I believe he will change if he truly wants to. I also believe my love for him was necessary, and I’m glad I loved him genuinely.

Now, I just want to forget about him. I still think about his well-being, but I have no intention of going back to him or being his friend either. I endured so much disrespect during our 2yrs rs that I genuinely hope he doesn't reach out. I just want to stop caring. I don't want to hate him because he also helped me when I was struggling mentally.

Any advice? How long did it take for you to trust someone again? Please be kind. Thank you!