a book with obsession as a core theme.

i'm looking for a book where the main character is OBSESSED, preferably with a woman, and it can be interpreted as romantic at first but as the book progresses, the line blurs, if you know what i mean.

the mmc should be either a pathetic little shit who loses his mind at the thought of the woman he's obsessed with, but can also be aggressive and unsettling. so like, i want yearning but in a VERY unhealthy context.

thank you!