There's 3 possible ending that I can imagine:
The MC accepts Nishino
The MC is already with a relationship with the Yankee
The MC doesn't really feel anything towards Nishino
I guess you guys can imagine your own canon ending :L
Holy shit this sounds like the story that my teacher once told. The guy in my teacher's story succeeded in suicide tho. This situation is truly heart breaking.
Is the GM his father because they look the same and his grandpa has the same hair color. But I doubt the chances are high because the GM didn't really show any emotions towards Kaname.