It is very normal to grieve after a loss. And it is natural that you associate the city to the relationship you thought you might have. Any time you have a relationship that goes bad, there are going to be associations that remind you of what happened.
The most important thing to remember is that your feelings about the city are probably the feelings you have for the love you thought might have been. The city itself has not changed, it is the relationship that made it all appear different. Before the relationship, the city was just a city to you. But since then, the relationship changed everything. So it is the relationship that is your real focus.
Focus on how you feel about what happened. Allow yourself to feel the grief. It doesn't feel good and it's hard to cope with, but moving through grief is the best way to get over it for good.
Learn what you can about the grieving process. The more you know, the better equipped you are to help yourself through this. Here are some resources to help:
Get as much support as possible. Friends, family and even support groups can help you get through. Talk about how you feel and if you like to write, start a journal. This will help you see your healing process and make you feel better.
Also, write a letter to him. Don't send it but just write about how you feel. Don't hold back. Keep the letter and add to it. Then when you feel ready to move on, tear the letter up or burn it. It can signal the end of the relationship for you.