Broke up with borderline gf after 6 years

I met her when I was 21, and it was like any normal beginning of a relationship of two young people just entering their 20s. At first, we didn't know about the bpd, but she did have severe abandonment issues and trauma from early parent divorce and a problematic estranged father, but I put that aside because at the time I saw it as something we could fix together.

Overtime, due to her mental illness, the relationship started become as toxic as you can imagine. She made me cut contact with every single person I've known before her, including a year of estrangement from my own family. She was violent towards me, controlling, jealous, financially frivolous and abusive in any way you can imagine. In moments of clarity, she was extremely sorry and said she had no idea what possessed her.

By this point, someone who doesn't know her would say she's a bad person. But there was more to it than just the bad parts. Her family are very mature, good and stable people. Her mother saw me like a son and was always on my side, thinking about how to help both of us. But I still had a child mindset and I absolutely did not have the tools to deal with it, that's why I let myself be abused to such a degree. Nobody was taking care of me, and I was going through this completely isolated and alone.

I knew that underneath everything she is a good person, just very insecure. She would admit all of those things and was hyper-aware, but during "episodes" of panic or mania she could not contain her feelings and inner pain.

Fast forward to around 4 years of dating, we decided to move to another country temporarily so she can try studying internationally. A fresh start in a new place, free of "triggers".

And then something happened. She suddenly stopped being actively toxic towards me. She stopped caring who I talk to, what I do, and genuinely told me she got over most of it. From one extreme it became another, to the point we had nothing shared between us, only our relationship quirks, but that's it.

But there was a reason for this change. Out of her illness, she shifted her obsession with me towards other guys, and she did to them exactly what she did to me. She never slept with them, as she had this sort of emotional block, but she did become romantically involved with them instead of me. I was extremely hurt the first time it happened but I forgave her. We both realized that she did it because she didn't want to hurt me anymore because she truly does love me behind all the neediness, but also because she wasn't afraid I was going to leave her anymore, being how "stable" of a person I am.

And then it happened again, and now it happened again. This third time, I told her I want to break up, and I understood that I was already resented since the first guy, and essentially almost since the beginning of the relationship. It may be hard to believe but she is dealing now with the stages of grief pretty good, and already reached a sort of acceptance with me, although she still wants me in her life (aka "bargaining"). Her mother and family are of course heartbroken and my parents and family couldn't be happier...

Now's is part where I talk about myself.

I hate myself for feeling this bitter and resented both with her and with myself. I know it wasn't on purpose, but I feel taken advantage of. Despite all the good times we had, the laughs, the travels, I feel absolutely awful. I feel like I've wasted almost the entirety of my 20s devoting myself to another person, completely giving up on myself. I have no idea yet what's up with all my friends back home, since I'll finally be back there in a few weeks.

I missed seeing them grow and growing with them together, I missed the liberty of early adulthood, I missed it all. I am essentially experiencing grief not just for her, but for all the lost time. This emotion of bitterness and resentment, I don't know how to integrate with it. How will I explain this to my past friends and people I knew? Will they even want to return in contact? How will I start dating again? I have no idea what people look for at my age of 27 because I'm so late to the party. I feel like I want to experience what casualness is like, but I'm afraid girls my age will look for commitments which I'm now terrified to give.

I hope she becomes better and shows everyone that she overcame her mental illness, as she is also exhausted for what it made her become, and would do anything to solve it. But I'm so tired of everything being about her, and never about me.

So how do I deal with the feelings I'm feeling? How can I get through this?