I Remember What You Did (Ghostbur X Quackity)

Au where Quackity and Ghostbur get together after the destruction of L'manburg. Except Wilbur didn't have his memory to start, and regains it only to remember what Quackity had done to his past self.

Or Wilbur remembers Quackity was his presidential opponent and worked with Shlatt. And takes time to think on things.

Emotional Hurt/comfort
Remorseful Quackity
Happyish endings