My guess is that MC didn't forget that his world's Dad is the SU Dad. SU Dad goes back to his world and the Real Dad comes back - it happens when Dad asks Sis IF he hurt her and apologizes. The point is that MC doesn't realize that Real Dad is back.
That's what I understood, BUT I might be wrong.
Anyway, I have the FEELING that the milking is so "strong" and the development so slow, that the Author Himself often forgets what the game's characters say, think and do. His whole point is that he HAS to build a HUGE, THICK, POINTLESS WALL OF TEXT instead of CGs, pictures and plot development. So, he just forgets what the characters say and think.