As Usher would say, “let it burn.”
Haha, but really.
As you’ve probably heard over and over again, living in the present moment is the key to happiness. You can’t control the future and you can’t change the past, but you can choose to be fully present here and now in order to make the best of things.
The past only lives when you constantly entertain the idea in your mind, so, although it’s easier said than done, focus your thoughts on the present rather than reminiscing in what doesn’t exist anymore.