If your ex took up a large part of your life, you are going to have to start building a life for yourself, a well-balanced life that brings you happiness.
First, take up a sport and get exercise every day; start by walking 2 miles a day.
Then, you will need a couple of hobbies, intellectual interests, a volunteer project, time with friends, and so on......
Start building a life for yourself full of positive activities. It will become fun and places to meet new people all the time.
Best wishes going forward,