morally grey relationships

Tropes: Step-siblings; Forbidden love.
Koi Nanka Shitakunai is one of the few stories I've read where the "misunderstanding" for lack of a better word, is reasonable and creates a thin veneer of tragedy. The morally grey bits are the fact that they are stepbrothers, and one is several years older than the other.

Tropes: Teacher x student;
Koi Ni Nare! is the "side story" that takes place at the same time as Koi Nanka Shitakunai.
The high school student-teacher trope is an ick unless it's done right and I felt this one met my personal criteria.

What I enjoy about this story is that the relationships are nuanced. Do we fault the people with personality disorders for behaving like people who have personality disorders? The MC and the ML both have dark histories. No spoiler so...I consider this "relationship" morally grey because they both have their reasons for their behavior. The person who has done the most damage is...............

This one is weird, I don't know how to feel about it. The boys are around the same age but it gave me (to a much lesser extent) the uncomfortable feeling I had when I read Lolita.

The pairing in Lover Boy is interesting and I'm not sure I ever really got over it but the fact that the older partner is the bottom somehow relieved my mental anguish. The MC has known the MC since he was a child. I believe there are 9 years between them.