Breaking up is hard to do, but fixating on your ex and your old relationship isn't healthy. You probably know that, but if you shift your thinking about your old relationship onto you and your needs, rather than your ex and the things you don't have anymore, you can start the process of moving on.
Whether your breakup was because of distance, death or infidelity, it's no use wallowing in what is no more or what could have been. Instead, focus your energy on coming up with a list of what attracted you to the other person and what you enjoyed about your relationship. You should quickly be able to see that the qualities you want in a partner and romantic relationship can be found in others, and that your ex isn't the only one who can meet your needs.
Even if you're not ready to date yet, coming up with a list of qualities turns your attention to future possibilities, and puts the focus where it should be -- on you. And once you are ready to dive back into the dating pool, you'll have something to hold onto as you navigate potential partners.
How to Get Over Someone [The School of Life (YouTube)]