You’re already saying that you’re going crazy, so why are you still fighting for this relationship? It’s no longer worth fighting for. You don’t need to be confused because it’s already clear that she cheated on you. She chose to be with someone else while you were still together, and there’s really no reason to continue.
I think it’s better if you ignore her and start over. Learn to love yourself again and focus on your own life. Keep yourself busy, spend time hanging out with friends, or even flirt and meet new people just to help yourself move on. I know it’s difficult, but you need to let her go because she’s no longer contributing to your growth, and your mental well-being is already being affected.
It’s time to move on.