Look at his sigh.
All I know is that I would have lost it there. And even if I was prez, I wouldn't have cared...presidents are people too.
But, it probably was better that he try to keep a lid on it right then for the sake of everybody else there.
I think President Bush left quickly for a variety of reasons..he was emotional (Reagan is his role model and he adores the man), he wanted to keep it dignified, he knows this is about President Reagan and not himself, he didn't want to hold up the crowds that had been waiting many hours to pay their respects, and last but not least, he and Laura were on their way to see Nancy Reagan at Blair House. He handled it just right.
I have a different take:
I think Bush tried to keep it short and not break down so he wouldn't be accused of using it as a "political" photo-op (even though I don't believe Bush would have even tried to suggest such a thing). We all know that's what the dems would do, so that's what they would accuse Bush of doing.