So, watching that Keith Vlog was really interesting and cute *laughs* I can see the boy having some attachment issues there. But the thing that made it touching to me is the implicit fact that Shiro is VERY important in Keith´s life, in many more ways than we thought.
For someone with the attachment issues he sure has (I see an avoidant personality in his character), being able to express, talk about feelings and openly state they need or love someone is a huuuge thing. Someone must have made a hard work “rehabilitating” Keith (hope that person is Shiro!).
If I remember correctly, Shiro is constantly asking Keith if he is Ok, probably because he knows him too well and knows that he must keep remembering Keith to express his thoughts, to talk, to not keep things that bother him to himself.
I can see Keith being really hard to reach when they first met, but Shiro never gave up on him and eventually earned his trust.