What if my avoidant ex gives everything I wanted to the new person?

I met a girl who was in a toxic, violent unsafe relationship, we ended up catching feelings or at least I did while she was with this man, a year goes by after meeting her and she finally did leave him so her and I tried being together only 2 months after her escaping said relationship that was 7 years long. I'm not proud of the things I did in that year and I pay dearly for it every day. Anyways when we finally got together it was great for only 1 month and I found she was pulling away where all I simply wanted was time spent together and she could barely handle once a week, eventually it was a constant battle where I tried to self abandon my own needs to please her and I just couldn't do it and the "relationship" failed. Naturally I blamed myself and it's been about 10 months since it ended, I found out she's been intimate with several others in the first 6 months of her being single and just recently I ran into her out with her new boyfriend, she told me he makes her feel safe....the same thing she once said to me. As a man it's hard to not compare and wonder why him and not myself? I tell myself that she will treat him the exact same way she did me, to make myself feel better but I just don't know. I've been working really hard on myself, I haven't been the same since her and I ended. How am I supposed to accept that she will give him everything I ever wanted which let's face it, was simply the bare minimum

ANY input is greatly appreciated Thank you and God bless