Textbook case of 'bait and switch' here.
He KNEW that sex was very important to me and he KNEW that lack of sex was a dealbreaker and that I had already left someone because of it.
Just like I knew the very first time we had sex, that his inability to cum inside a woman would pose a serious problem down the line. (Wish I could say I walked away there and then but...damn chemicals.)
Anyway, I had already had an experience with sex dying around the one year mark, so I kept my eyes open. This time it was even worst. He managed about 8 months when sex became a monthly occurence practically overnight. By year three, sex was as dead as a dodo bird.
The problem is not the bait and switch per se, because there's no way to avoid it. It's the fact that we don't walk away the moment we realize it happened, because by that point we are emotionally invested and still hopeful that "it might come back".
Come to think of it, a really savvy woman would have walked away back when we were still flirting and he dropped hints about 'past' gender and sexuality confusion. 'Past' as in, ok, I've decided that transitioning is too much of a PITA and being gay social suicide, so I will remain a heterosexual male.
Lesson #1: There's no such freaking thing.