Haunted by the past...How do I let it all go? Please help.

Hey everyone, my name is Elizabeth and I have really been struggling lately with coming to terms with the past and embracing the future. I dated a man for a very long time, and I was absolutely convinced that he was "the one". We planned an entire future together, but ending up going our separate ways in June 2015. It has been almost a year without him, but I still think of him daily. I don't miss him or desire to get back together with him, but I do find him popping into my mind very frequently. He now lives across the country with his girlfriend and it hurts me that he gets to move on, but I feel so stuck. I constantly finding myself getting upset about things that happened months and months ago. I just want to move on and lead a happy life without being confronted by thoughts of him. I have been working very hard to move on, but recently I started dreaming about him again and it has been really tough for me. Any advice would be amazing. Thank you for reading.