I (33M) am having trouble moving on from a toxic relationship with my now ex-girlfriend (29F)

TLDR; She cheated on me a couple of times, I don’t know why I still love her and struggling to move on.

Not sure if I am in the right place but I am at the end of my rope and don’t know what to do. I separated from my girlfriend and mother of my child about a month ago. The first 3 years of our relationship were amazing, and I fell in love with her pretty quickly. I consider myself to have high standards and finding a girlfriend was never easy because one little thing could put me off someone, but she ticked every box, and I was obsessed. After 3 years I proposed and a few months later she cheated on me with my friend and left me for him. I was devastated, never been in a worse place mentally. Really bad thoughts were constantly rushing through my head. After about 2-3 months their little fling had started to fall apart, the honeymoon phase came to an end I guess, and she came running back crying explaining she had made a huge mistake and didn’t want to lose me. I stupidly took her back because I was still infatuated and on top of that, didn’t have any confidence/self-esteem after the ordeal and didn’t think I could do any better because I had this vision that she was perfect and that I must have been a shit partner to make her want to cheat on me.

A few months pass and she falls pregnant, even though she was supposed to be on birth control(sus). I hadn’t even healed properly yet and 9 months later our beautiful little girl arrived. Throw a kid in the mix while trying to deal with the thoughts of her and my friend bumping uglies. It didn’t end well. I was all over the place. 3 years and 3 months later and she cheats on me again, with a random guy that had been coming through her work every day, obviously had been shooting his shot the whole time and she was more than likely welcoming it. I wouldn’t pursue a girl if I knew I didn’t have a chance, so he must have thought he had a chance. She breaks up with me, the very next day she’s seeing him. 1 week passes and they’re all over social media. 7 years with me and she moves on in 1 day, but not only that, introduces our 4-year-old daughter to him within the week of leaving me. Also had him move into our house immediately so our daughter went from waking up to me in our bed, to waking up to him in our bed. I was furious and even more destroyed than the first time round. I never got the chance to heal from the first break up and now had to deal with this shit. This lasted about the same time as the other fling, 2-3 months, the honeymoon phase. This time however, he had a wife that he was cheating on, with my then ex. My ex had no idea that he was still seeing his wife as he told her he had left his wife. Karma right!? So she gets a taste of her own medicine and I have never seen her so upset in my life, which also really bothered me because she never got this upset over me. A few months after they ended their fling, she messages me asking if we can talk and I stupidly agreed, I really am an idiot. We get back together for a year and to be completely honest, that was the worst year of my entire life.

I ended up leaving her a month ago, and I can’t get her out of my head. I can’t get anything out of my head. The cheating. Vivid thoughts of these guys fucking her. It didn’t help that there were videos of their sexual encounters that must have been backed up onto my PC when she connected her phone. I feel like I will never do better, because she was so charming and beautiful, and I thought she had a good heart and can’t understand why or how any of this happened. I resent this girl so much but love her so much at the same time. I have done so well keeping contact to a minimum and only discussing our daughter. She has begged for me back countless times and I have said NO.

I just want to move on with my life and get this out of my head. Any help to step in the right direction would be greatly appreciated.