When you are sure it's over, it's time to start a new life. Get excited about being a better you, and happiness will return in time!
Something that helped me, my sister said, "you're at A and you want to get to C, but you have to go through B first." What you're experiencing is unavoidable. You have to feel pain before you feel better, but you will!
Agreed on working out, etc. Take time now to do things you've always wanted to do but never did. Have some fresh experiences alone or with friends and family. Make a day trip and go canoeing or hiking. Get out of your element. It's time to live again, and that's something you can do alone, believe it or not.
And if partnership is what you want, you'll find love again, in time. The sooner you feel good, the more attractive you'll be too, so just relax, do new things, exercise, have fun, be productive!
Edit: get off the social media, throw out or put into storage photos of you and girlfriend, etc. put the past behind you and move into the future!