I had a haircut after my relationship ended. But my reason was different. I was not allowed to cut my hairs and they grew so long that I used to get headaches because of the weight on my head and they were too difficult to manage esp in the garmi of Pakistan.
But it did make me feel good everyone told me that it was a good change in my appearance.
Go on have a hair cut. Buy some new cool outfits. Go have some amazing food. Do things that you enjoy and that makes you happy. Your life should be about YOU. Treat yourself well !