Was at my peak mentally, watched myself slip into rumination over separation in 2024, currently feel adrift

How do I snap out of it?

I'm constantly thinking about my ex. I wanted to say something, and she didn't give me the opportunity. It felt unfair. As if what happened liberated her and she had no interest whatsoever in reversing it. All I wanted to do was speak with her one last time, but she avoided, ghosted and deflected. I hoped I'd brought the point indirectly across, but I likely didn't, and the rumination was unbearable.

Subsequently, I'd see her in public in random places, and I'd always catch her staring too late. Missing the opportunity to talk. She never reached out.

2024 has been hell. Straight up schizo rumination hell. Emotional roller coaster. And for 2025, I've wanted to return to my old self. I feel like I've changed so much, and I don't know how to let go.

My original lamentation: that desire to apologize to her. To achieve clarification, make sure she knows my side, which is genuine and appreciative. Make sure she doesn't think I think poorly of her. Just to air things out between us and make sure we are on the same page, so we can both walk away with our heads held high. She is not interested in this. She moved on a long time ago now.

How do I let go of this obsession?