Marinette is a forgiving person, so when Chloe seems to have finally changed for the better Marinette forgives her, with a little hesitation. But Chloe never changed. She rips Marinette apart one night and Marinette after recently taking another, harsher, indirect rejection from Adrien decides that the world is just better off with out Marinette so she transforms for good. The only time anyone ever sees Marinette is after Akuma fights when she needs to get cookies for Tikki.
Adrien, even though he loves Ladybug, misses his good friend. He decides that the police aren't trying hard enough to find her. So he transformed to go look for her leaving a note on Marinette's desk telling her that he, Adrien, wouldn't come back until she did.
Chat ends up finding Ladybug and confides in her about it and she gets mad and storms off. Marinette, not knowing where else to go, went home. She went home to find Adrien already there, sobbing on her desk, clutching a picture of Marinette in his hand.
*****
So I had this idea before season two was completed. I know there are a few other books like this, but I want to let you guys know that I had this idea before I even got Wattpad. I am not a plagiarist, I may write fanfics but I always give credit where it is due.