[He focuses, instead, on how distant that smile feels-- notices it only because he's not used to that sort of look from Keith, even if there's fondness there. He looks down, breathing out, managing a small nod, too.]
Yeah.
[But that's just it-- getting what he wants means not what's best for Keith. Even if Keith were to return his feelings, well-- he deserves something better than what Shiro can give him. And going for what he wants, in this case-- it would only make Keith unhappy, either way; either he returns his feelings and Shiro messes it all up or he doesn't return his feelings and Shiro puts Keith in an uncomfortable position as his friend. Either way, it's-- not something he can actively seek out.]
Keith... I'm not unhappy. [To actually answer your question. It isn't so simplistic as whether he's always happy or always unhappy, and he knows Keith knows that. But he's still going to clarify.] I'm a Paladin. I have a purpose. I'm alive. I have our friends. [...] You. I can't be fully unhappy if that's the case.