[He can probably feel how much Keith is trembling just from the touch on his shoulder, not shifting his eyes away even though he looks like he'll completely lose his nerve and break away at any moment. As it is, his mouth is dry again, uncertain but - it's there, and he can't, won't take it back. He nods again, and even though everything about his demeanor and even his tone of voice should be wavering or unsure... when he speaks it again, there's the pure unfiltered truth of it to carry the words and really drive it home.]
... Yes.
I'm in love with you. [He didn't bother to read when the words last changed, so this just kind of unintentionally solidifies it:] I have been, for... a long time.