Sometimes I feel sad of being alone after a 6 years relationship. I still have this bitterness?

I don't want to think of my ex anymore. We broke up a year ago but to be honest, Im still recovering since its just recently that I decided to move on and not to talk to him anymore.I know I did the right thing. But there are times when I miss the times when we were together. I hate that feeling. And I see couples very much inlove, I feel depress, but not all the time..So any uplifting advice