What is the best way to break up with someone?

My best friend and I used to be a couple, but were also friends before this. We had an awful row and I smacked him in the face. He left that night, our relstionship was over. When we had both had time to calm down, we realised that our friendship was worth saving. We are not a couple but we are so much closer now. We each still have our rough times but we are always here for one another now and for that I will always love him and vice versa..