The Truth From Which You Run
Harry is dressed in the yellow-and-black of Hufflepuff House, and Blaise is surrounded by silver and greenharryharryharry… They still see each other in some classes, and when he hears about Snape telling Harry off for anything at all that can't possibly be his fault, Blaise's eyes harden, and he logs each incident in the little black book he keeps in his head.
He'll repay every entry double one day.
All the teachers turn a blind eye to what really happens when both boys go missing from their dormitories at night. McGonagall frowns, but grudgingly admits that if it's promoting inter-house relations, then she's not going to protest.
Even those who do see, like Dumbledore, pretend not to. No, the truth is too disturbing, they're only children… But it's the truth, and no amount of denial will change that.
Dumbledore knows it well. And that's the only reason he doesn't kick up a bigger fuss when the Minister claims that Harry's mental state is too fragile for him to be surrounded by so many people.
Harry is moved into the permanent resident's ward at St. Mungo's, and he doesn't understand well enough to protest, even when Blaise runs after him to say goodbye and they hug so tightly that neither of them can breathe but they don't know how to let go until the Ministry witch pries them apart and he knows that Blaise is his last link to sanity.
And then he is gone, because he never had a choice.