She can cause she probably emotionaly deteached from you months or years ago. When i was in my 4 year long relationship i moved on after a week cause i emotionaly deteached form my ex months before we split up. Didn't have any feelings toward him. I am sory you are going through this but sometimes when people are not happy or they don't know how to fix relationship any longer they will emotionaly deteach before they break up for real. Hope you are doing well and safe.
