Endou-kun No Jikken Note
Torikago Syndrome
The problem with shounen ai and dark/psychological manga is that there're a lot of hints or suggestive scenes, but you can't be sure what happened. For example, the incestuous relationship between Kain and his mom or his twin brother, Litch. There was scenes that would suggest Kain's mom had sex with him because his shirt were opened, but maybe she abused her son in non-sexual way. Yaoi would give more impact to this kind of tragic story, make the scene seems clearer without interpretation by the reader, like Acid Town, which obviously indicated the rape really took place, or the relationship between the twins.
Ren'ai Houteishiki