He abused the Uke mentally and sexually, is isolating him, to destroy his mental health even more and the Uke only stayed with him, because that scum would've taken away his son otherwise. After he destabilized his mental health so much the Seme and everyone else can't blame the Uke to belive what the Seme's father said. Don't forget he also heared that secret conversation with the doctor. In the end the Uke doesn't trust anyone now and just wants to run away with his son
So first of all I'm sure if it was a side story or just a normal oneshot.
The story is like this: it's the MC's Birthday and his boyfriend is with him, everything seems fine, but then the focus is more on an accident that happend a year ago. The MC's boyfriend died while rescuing two children.
In the end it turns out that the MC talked to himself the whole time, because he couldn't see his boyfriend (ghost), then he goes to a cliff and jumps off asking why his boyfriend was taken away from him, while his boyfriend (ghost) is next to him crying and begging him not to jump