How did you cope with heartbreak?

I lost contact to one of the sweetest guys I never met, after only 4 weeks of constant talking.
It's been 9 weeks and I still think about him all the time and seem to be unable to let it go.
Things ended extremely unexpectedly for me, and it's still unreal to me that this is over.
Why is it so hard to move on and how can I let it go in a healthy manner?
How did you cope with heartbreak?
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