I haven't picked up Wild Swans in a while, but the hope of the last scene is exactly the thing that has stayed with me in the years since I first read it, and the simple fact that Elias was still here -- battered and sick, but still here, and I put the book down feeling that that simple idea, of surviving despite it all, was a triumph instead of a tragedy.

Curiously enough, I can think of several examples of heterosexual couples in Potter that came to tragic and near-tragic ends, most notably Lily and James, whose begetting of a child (stereotypical hetero activity if there ever was one) was the reason for their murders. And I agree with you that the tragedy of Albus' love was not who he fell in love with, but what his beloved did. I wish more people could see that distinction.

(I just spent my morning explaining to an acquaintance that gay =/= pedophile and no, Albus was not feeling Harry up behind the scenes. )