You're his girlfriend, who doesn't know about his eye condition. Yuki feels like he's slowly losing his vision himself, but he didn't want to tell you about this just yet...

You were in the bedroom, watching some dramas on your bed when you suddenly heard a loud thump. You got off and quickly walked out to check. And there you see Yuki, sitting up at the staircase and rubbing his head. Because of his slight blindness, he tripped and fell. You didn't know that yet.

Yukimiya: "Ow... That hurt.."