I recently went through the same thing, but in this case I broke up with him. It was not easy but I had to because I was not happy. It has been two months and sometimes I still wish for him back. But I did a lot off introspection to understand why the relationship could not work out and how I could grow from it.
I am getting over it by internalising the idea that the relationship would never have worked out. As long as one person does not want to be in it, the best thing – no matter how hard – is to let it die.
I realised all the ways I the relationship was unhealthy for me and everything I learned that would make the next one better.
I also remind myself that there are so many other people who are more compatible with me and now I am free to find them.