How do I get over my ex?

Posting this here because I'm unsure of where else to post something like this.

Over two years ago at this point I mutually ended a nearly year long relationship with someone I was still in love with. We were graduating high school and while still going to colleges in the same city, realized we were in over our heads and were in an unhealthy situation so we split it off. It destroyed me. It took me a year to get my shit together (I went on a minor drug-binge for about 3 months after and spent probably $6k from eating out and making sure I always had enough bud) but I eventually met my current partner. Things aren't perfect in our relationship but I genuinely love her and we work to further strengthen our relationship. I don't know that I see the rest of my life with her, but we've been together over a year now and I don't have any intention of ending things anytime soon. We also live together so making it work is more of a necessity lol.

But I can't get my ex out of my head. I've spent nearly every day for the last two years trying to let go of her but I don't know why she keeps popping into my thoughts. I don't love her, I don't want to be with her, I don't want her in my life. And ahe isn't, but I'm still dealing with this. I do have a therapist who I've talked at length with about this but I don't know, something about her just is stuck in my head. Maybe I preferred sex with her? I doubt it but she did kinda define what I consider my "type", so maybe it's just she's more unromantically attractive to me? But it feels so much deeper than that. If it were those shallows reasons I feel like it would've been easier to debug and diagnose. She was my best friend. One day she was in my life, the next day not. It feels like a very specifically sized puzzle piece is missing and now there's a small hole in the puzzle.

I don't know, it's kinda maddening. I don't have most social media, so it's easier to avoid her online and not think about her. But occasionally I find myself borderline stalking her, except it's just me gathering random information I already know from OSINT tools with no intention or idea on how to utilize it (I'm well aware of how to use OSINT data, I mean in this specific situation). Part of it just feels like someone really important to me was rapidly removed from my life and I yearn to reconnect with them, but I guess I fear what such an endeavor might reawaken in me. I don't love her, at least I don't think I do. If I do it would be monumentally fucked up and I would feel like I'm emotionally cheating on my partner, who is somewhat aware of this issue but thinks I have it figured out (I thought I did too; I'm not knowingly lying to my partner). I don't know, I sent them a proper goodbye email a few months ago and thought that was that but it's clearly not. And I've put so much time and effort into trying to wrap it up for myself but now it feels like I'm just lost and stuck. Part of me just wants to reach out and ask if we can get a cup of coffee, but the other part of me recognizes the red flags in that immediately.

I just want to be done with this. I want my brain to get it through itself thar it's over. It's been over. There's no changing the past, and if I could, I don't think I would've reached the point where I am in life with my current opportunities if we had stayed together. Part of why we broke up was because as I was learning how to sell pot (which I was never very good at), I became a massive stoner (which I am very good at). She wasn't anti-weed but didn't appreciate it. When eventually saw that us growing apart was hurting each other and decided to leave things behind. Being young and dumb, I didn't handle the breakup well. I didn't do anything bad or harmful to her or anyone else, but it was obvious to both of us that I wasn't okay afterwards. When I feel like I needed her the most, she was gone from my life. In doing so she broke our promise of prioritizing our friendship over the relationship. I don't really know. I understand a lot of the reasons why I'm hurt and some are justified some are not. I understand the role I played and the responsibility I had in hoe things ended. I was not a great partner in a lot of instances, and neither was she. But part of me wonders if we had met now what it would be like. But I wouldn't have been who I am now without her and without being without her. I'm just so fucking unsure man.

I'm sorry if this is really rambly. I expect that the majority of answers will probably be to just get over it already, which I'm trying to do. I just don't feel like it's the right thing to ask to see her again, because that feels like an eventual mistake rather than closure. Idk, tell me I'm an idiot or an asshole to my current partner or something. I just want to be done with dealing with the legacy of a long-dead relationship.

TL;DR: Mutually ended a significant relationship when I wasn't ready. Been kinda fucked since. Want to not be fucked so I can be a better partner. I suck for this.

Edit: Thank you to everyone who has commented thus far. A lot of the discussion has been really helpful and I've got some new leads on how to debug this issue. I'm trying to respond to everyone and I can't express how appreciative I am.