I went through a similar thing about 15-20 years ago. I’ll tell you it wasn’t easy, and I had some pretty strong emotions for a year or more afterwards.
The things that hurt the most were going places or doing things that we used to do together. Thus the things that helped the most were the opposite. Pick up some new hobby or activity that you’ve always wanted to try. Especially those things that you wanted to try but you didn’t because your ex wasn’t interested.
It’s also a great time for self-improvement. I started eating better, riding my bike, rollerblading (hey it was more than 15 years ago :-)), and stuff like that. I ended up dropping about 20 pounds, and it was quite an ego booster to be turning women’s heads.
I also took a few classes at the local community college. You meet a new crowd of people, and learn some things while you’re at it.
One of the smartest things I think I did was not start any serious relationship for about 2 years.