Learn to move on from that which hurts you. I wouldn’t say you should let go, cos the truth is, we don’t really let go of certain memories, no matter how hard we try. We might think we did let go, only to find ourselves being reminded of them, probably by just a gesture, a person, or even a thing. So, yeah, letting go is out of the question.
The best you can do is move on GENUINELY, that, whenever those sad memories are revived from their subconscious, you wouldn’t give a tear or feel a pain in your chest. Rather, you would give a smile and contented sigh that says “that was just life being life, I’m better now”-This is one way to ‘forget’.
P.S: Make peace with that sour past of yours, and you’ll realise just how less stingy it feels when reminded of it.