In a somewhat similar situation to you myself. I can't exactly tell you what got me out of it completely because I'm not there yet, but I can tell you about the progress I made so far.

Fundamentally I think it's important to understand how the human ego works. The ego looks for external things to create an identity for itself which you will translate to 'who you are'. It hurts when your ex leaves you in part becuase you lose your identity. You will have invariably derived some confidence from having an SO and may have even began to adopt their qualities as your own. Have you ever caught yourself wanting to brag about her to new people?

This is really dangerous psychologically and being single should give you the opportunity to derive confidence from yourself again. This is another slippery slope however, you can end up identifying with the 'single independent guy' which can cause tensions in the early stages of a new relationship as that identity is challenged.

The key is to not search for happiness in abilities or forms (physical etc). It is possible to be happy with your life situation while also striving to improve it. It's difficult to detach the ego, and the first steps are to 'watch' your mind and spot how it works. What gives you confidence? What makes you happy? What makes you feel insecure? Are you happy in the moment or do you spend your time perpetually thinking about the past or future? Understanding the answers to these questions is the first step to finding peace within yourself

A lot of this stuff goes way beyond relationships.

I cant profess to have all the answers, as I'm still trying to get there myself. If you're interested in learning more about this topic I highly recommend eckhart tolle's books.

Good luck brother.