How do you get over a 10 year relationship that ended in ghosting?

I think my ex was just done. We had been fighting for a while and I started drinking again. I was really drunk and I went out and I slept with a Coworker. My ex and I were long distance and that was the biggest thing that we fought about. It’s been almost a year and I’ve never felt this low since my first dog passed away. But even during that, somehow I healed after 6 agonizing months. This is like a permanent grey cloud hanging over my head. All I do is sleep. I’ve lost all will to function. I couldn’t even accept it was over until now and I feel even worse somehow. So how do you move on? How do you forget someone you spent almost all your 20s with? Gosh I met my ex when I was 17. It fucking hurts.