Suffering over my ex

I dated someone briefly last summer and I still feel sad about our breakup. I try to shift my thoughts but I still feel hurt by how he ended things and there’s a lot of pain that comes up when I think about him. I keep thinking time will make it go away but I still feel pretty miserable. Do I let myself sit in this feeling or should I try to change my thoughts around it? There’s part of me that thinks I shouldn’t still feel this bad after all this time and I think that thought is making it worse.