Thought I was over it

Was broken up with about two months ago from an on/off relationship for a few years. I thought I was slowly over it and accepting it all but I just randomly had a break down. Sitting on the couch watching our Sunday funday shows and realizing he's not here to complete it all. Sigh, do you ever just miss someone you know you'll never be with? Any suggestions to get him out of my mind? I feel extremely sad about (the PMS may be a reason)