I know your comment was written a while ago but yeah you essentially had it. The guy at the end is a man who becomes essentially bewitched by Sana, who has become a creature like Iza was. Iza in turn has become more human as Sana loses her own humanity. So he does ultimately truly love her but she lacks any ability to reciprocate that love. Idk if you’ve read the main story, but without it you lose a whole bunch of context. It’s a tough read tho because you see how deeply Iza traumatized and isolated Sana so that the only being she had to rely on was him. He continually kills everyone she loves from her father to her husband and a ton of people in between.
I read this 'till the end, and all it gave me was confusion. What the hell happened to Sana and Iza on the last chapter? Who are those guy? Does that mean it's been a long time that Sana and Iza became some kind of legend but this still living and remain hidden to that day?