Block his number.
If you can't get yourself to block it, at least remove his picture (if you have one) and change his name to something funny. My ex is DDI for Don't Do It (meaning call him or text him). That one does help.
I got into doing things I admired in others. I run almost every day. I am training for a century (100 mile ride in a day). I rock climb. I am making life so interesting I don't have a bunch of down time to get squirrely and wonder why he doesn't call or I don't have someone else. The exercise has the side benefit of getting me fit and looking good and endorphins.