SOLVED. About a man obsessed with his ex-girlfriend and kidnaps her child [s]

[Jess]

Very dark book - protagonist presumably has a mental illness as he sees a psychiatrist, is obsessed with his ex-girlfriend even though she is married with a child, he is a primary school teacher who loves poetry and reading in general, he is friends with a prostitute who's name I am pretty sure is Angelique, but maybe not. Written from multiple perspectives starting with the protagonist's psychiatrist, second perspective is from the husband of the protagonist's ex-girlfriend.

[Jess]

I started reading it about two years ago but stopped for some reason or another and I'm dying to pick it up again. The cover was almost all black but for a partially opened door with blue light filtering in, the title was I think in the top left or right hand corner. I'd say it's meant for an adult audience, quite a bit of explicit language, adult themes etc. The book starts with the protagonist's psychiatrist describing his (the protagonist's) life as he knows it: he is a primary school teacher, lives with a prostitute (I think named Angelique) who loves him, he is obsessed with his ex-girlfriend who is married with a child. Sometimes he goes to her house and watches them through the backyard window. Once when he was in the backyard her kid was swimming or something and started drowning so he saved him.
He was defamed as a primary school teacher because he began tutoring a kid named (I think) Carlos after school and one day when Carlos went to the bathroom (and he hadn't told his parents he would be staying after school) he didn't come back, he disappeared, and it seemed like it was the protagonist who committed the crime. Eventually left the school.
At the end of the chapter with the psychiatrist the protagonist kidnaps from school his ex-girlfriend's child.
Second perspective is that of the ex-girlfriend's husband. There is tension between him and his wife because her ex-boyfriend just kidnapped their child but came forward saying the wife organised for him to collect him or something. He has been seeing prostitutes even before that, one of them being Angelique, coincidentally. He justifies it by saying other people in his business do the same thing (or something like that), all I know is that he tries to vindicate himself for it. I think he works in stocks?
Also, the psychiatrist speaks in second person narrative, talking to the ex-girlfriend.

Help, please?

[Andria]

Seven Types of Ambiguity

[Jess]

Thank you you perfect human being!