I totally understand the being "left behind" in the house feeling. In the beginning I was completely envious of my ex being able to just hit the full on reset button by starting in a new town, new space and with new stuff. I got over the house part eventually as I was in it before her but the biggest thing for me were the activities we would do together. Boating, going to races, our weekly restaurant visits and things like that. Those are still my favorite things in the world to do but for the first year or so I had no desire to do them because they were "our" things.

Now I make sure to spend time with friends and remember that times were and they can be again, they are again. Things will get better.