Self-improvement. Tell yourself "Self, we can do better. Let's get some." No need to buy a gym membership, but it's a great time to re-evaluate what you eat and why, how you exercise and why, and what's important to you and why. What hobbies have you let slide because she wasn't into them? Revisit those. What music haven't you been listening to because she hates it? Cue up that playlist. What places have you wanted to visit but haven't because she was lukewarm? Plan a voyage. This is a chance to revisit "you as you" instead of "you as reflected in someone else." There are aspects of your personality and self-image that have improved because of her. Embrace those and welcome them. There may be aspects of your behavior and regard that have degraded because of her. Dismiss them. One of the golden-age movie moguls used to celebrate whenever a famous person died because that meant they could finally do a biopic; without an ending, you can't really put someone's life in perspective. Now that your relationship has an ending, you can put it in perspective - what was it good for? What was bad about it? What will you miss? What will you not miss? There's a psychological process we must go through before we are ready to be with someone again. It's a process of recentering, re-evaluating our wants and desires and reacquainting ourselves with ourselves. The people we are after a long relationship are not the people we were before a long relationship and our two selves must meet, get to know each other and merge. This is an active process and one which we must experience largely in solitude. Not to say you need to eschew the company of others, but recognize that the void you feel inside can only be filled by you. It's a you-shaped hole and only you know what to plant in it. Fair warning - this void you feel is visible from the outside. It can be sensed. It will be avoided by others. You will not find someone new (someone of quality, anyway) until you have filled it. Note that the more you fill it, the greater the content you add to your life, the more attractive you will be to external observers. Don't ask us for movies and music. Ask yourself a year ago for all that stuff you didn't get a chance to check out and check it out. Good luck. These are hard, formative experiences and no one enjoys going through them. I think we can all agree, however, that they make us what we are.
I've had two big breakups in my life. After each I have had huge self improvements. One of them I lost 30 pounds after.