Breakup guilt

I had a partner for four years. I was a physical caregiver to him (he had a disability), emotional support, we lived together during the pandemic, and I started realizing I wasn't feeling very happy or fulfilled with him. I would cry while being intimate and not know why. I would try to talk about needing to increase our emotional intimacy and communication. I was bored, tired, and sad, and even after conversations it felt like nothing changed. He also wasn't supportive of my move for school, but gave in eventually. And that was the straw I think that broke it all down, because I didn't feel supported. So I moved and once nothing changed I broke up with him. I stopped communication because I didn't feel it would be worth continuing.

I carried a lot of guilt because I was the one who took care of him. I gave so much of my youth to love him and make sure he was okay without thinking of my own dreams and goals because I was trying to do the "right" thing. Fast forward four months and now I'm feeling a lot better. I'm starting to embrace the things I really enjoy, learn what makes me happy, and I'm starting to feel stable enough and secure enough to start another relationship. I'm now talking to one of the coolest people I've ever met. I feel like I genuinely feel love for him, not just obligation, but like, admiration and love for the person he is. It's a very nice feeling.

Then I get a letter from my ex. A real handwritten letter. It essentially was a letter saying how miserable he was without me. How he tried to date someone else but he couldn't. How I was killing him inside. How I'm the only person to have ever made him cry by doing this. How he "doesn't miss sex, he just missed me" and how he thought we would get married and buy a house and start a life but I left with "no explanation".

It was a really painful thing to read because I don't want him to hurt, but I also know it isn't my obligation to help him with that anymore. I wasn't happy, I couldn't stay. I couldn't sacrifice myself for him anymore. I had told him I didn't think I had loved him for a while, that we'd had conversations about intimacy and how I was struggling, and that things needed to end. I figured that would be the end of it. But now I feel like I've ruined someone's life, like he's so depressed and miserable and it's my fault. I don't want to feel that way, but I just do. And now that I'm talking to someone wonderful, I don't want these feelings to get in the way of being able to develop a new relationship. I guess I need help on getting over the guilt. I feel selfish, but I know I had to do this for myself, and I'm feeling so conflicted and hurt again now.