I agree with you on the power of the relationship. Even for younger children who are reading it only as a friendship betrayed, the depths of the betrayal are horrific.

As to no indications of any non-straight sexuality, oh come on ... she even descends to goat jokes! But I do agree with you that this whole side of life is very much sublimated through the whole series, with Ron/Hermione being the best example of how much the war costs in personal terms.