Whether or not Stevens was gay, it’s not likely that the Islamists knew anything about it. He was killed because he was an American, and the ferocity of the attacks was because of that fact alone: he represented the West.
Incidentally, it has emerged that Stevens himself was a Muslim convert. He was a Sufi, which is regarded as a heretical sect by “orthodox” Muslims, but it’s not likely that the attackers knew this, either. In any case, Sufism is very opposed to homosexuality, so even if he had been considered gay at some point, he wouldn’t have been an active homosexual anymore and hence there’s no way al Qaeda could known about it.
He was killed out of hatred for the United States and the West, and also, as in the case of the Egyptian attacks, to show our powerlessness and the fact that we are now afraid of them and they can attack with no concern for retribution from us.
I think it goes deeper than that. just a feeling.
Someone sent me a link to a video about Stevens converting to Sufism but I can’t find it. Do you have some source/link?