❯Spoiler!

After he regains his memories he'll play along for a while longer, starting to subtly demean and insult FL (she questions herself whether she's just being paranoid since he mixes is with being sweet) before finally abandoning her. Goes on a while longer with the emotional abuse in the second half of the story.

 

That's the summed up less spoilery story

 

More detailed spoilers below 👇 

 

Basically there is a very important subplot with a cello and their past (without spoiling too much, he blames FL for a very significant incident in his past - yes they knew each other in the past and he came to the island to kill her in the first place). If I remember the finale of the first half correctly FL set up a cello and orchestra for him which he basically destroyed right in front of her eyes, poisoning the tree she loves so dearly, smiling while watching angry villagers attack her and then going to destroy her house, making her fall in depression all in all.