How do I move on?

Me (28M) and my ex (25F) broke up about 6 month ago. We be been together for about 8 years and the last couple of years have been rough. Some times during arguments we told each other that it is over this time, but at the end of the day we usually talked it out and continued on, but not this time.

A couple of days later after the breakup, I went abroad on a trip I planed for a long time and booked in advance. I was away for about 1,5 months. Under the first day I entertained the idea of our relationship truly being over, but I was still expecting us to get back together. After talking to her a bit more under a few days I realized she wanted to stick to it, and I just didn’t try to do anything about it.

During the time I was away, we had minimal contact. She moved out while I was away. When the trip was over I basically back to an empty apartment. I graduated that same summer, was not in the best place economically nor mentally since I’m dealing with GAD (generalized anxiety disorder).

Time went on and I did not really think to much about it, I started a new job right after coming back from my trip and was busy. Then, 4 month later, I found out she actually started meeting someone like 2 weeks after moving out. And that she pretty much lives with the new guy, and left our old dog, which was originally hers from the beginning with her parents in another city, which hurt me a lot because I miss him and did not even get to have a say in it.

During this time we have had no contact, I respected that she did not want to talk to me, but she wanted me to contact her if I found some thing at my place that belonged to her, and I also told her that I would like to help out with the dog among other things and that I still care for her. But I eventually noticed that she blocked me everywhere.

The thing is, I blame a lot of this on myself. She was a sweet girl and really cared for me. And I loved her, but I did not listen to her needs, i did not actually try to make this relationship work the last couple of years. I have my issues like everybody else and deeply regret our arguments and what we said to each other during those. But I know I was the asshole in this relationship. I know she deserves better, but now I feel that I have had some time to reflect and I realize my misstakes, but it it’s to late.

I would do anything for another chance, but for her, it’s like I never even existed. It hurt so bad, I’m mourning her and our relationship as if she has passed away.

But I still cannot help feeling self hatred, betrayal, anger and so many other feelings that honestly make me loose my mind.

I have been dating, and are meeting another girl as of now, but I still cannot get over her. It feels like I made the biggest mistake of my life, and that I will never find another person like her, my person…

How do I move on?

TL;DR: I (28M) broke up with my ex (25F) of 8 years six months ago. She moved on quickly, started seeing someone else, and cut all contact. I blame myself for the breakup, regret not working on our relationship, and feel like I lost my person. I’m struggling to move on despite dating someone new. How do I cope?