You be better. I'm glad she's happy now, because I think that's important.
I once messed up a "relationship"/fling with a girl I had grown to care about as a friend. She ghosted me afterwards and it absolutely devastated me for a while. Eventually, I reached out again and she told me she didn't realize I felt so guilty and that she wasn't upset anymore and hadn't been for some time, and that did help a bit. Still, I hate knowing that I was able to mess up that much. So, I try to be better. That's all I can do.
Sure, you could die because you messed up and hurt someone. Humans hurt people, and humans learn from hurting people, because for most of us it feels bad, and we don't want that bad feeling again. So, you can either get rid of yourself, or go out every day a little more determined than the average person not to hurt anyone, and to help other people feel good.
Punishing yourself doesn't actually help anyone. If you feel the need to punish yourself, doing it through penance at least will make the world around you a little better.