In relation to this question, I feel kind of like I imagine Gentile believers must have felt prior to the Council of Jerusalem (described in Acts 15).
Many members of the Church prior to that council insisted that in order to be a member of the Church in full standing, you needed to live the Law of Moses. It was then that the Church finally clarified that conformity to the Law of Moses was no longer required.
At the council, Peter testified: "And God, which knoweth the hearts, bare them witness, giving them the Holy Ghost ["them" being the Gentiles -- who were not conforming to the Law of Moses], even as he did unto us; And put not difference between us and them, purifying their hearts by faith. Now therefore why tempt ye God, to put a yoke upon the neck of the disciples, which neither our fathers nor we were able to bear?"
Ultimately the council issued a statement: "that we write unto them, that they abstain from pollutions of idols, and from fornication, and from things strangled, and from blood."
It's interesting to me that they said "that they abstain from... fornication." The gay community has been going through an evolution in the last couple of decades, and is in the process of rejecting promiscuity in favor of commitment and continence within the boundaries of marriage. We've demanded no less than "marriage," we've been very deliberate about insisting on that word, because the word "marriage" clearly defines the kind of law we desire to govern our sexuality. And I believe, in consequence, we're seeing the Spirit being poured out on the LGBT community to the extent that we're willing to let ourselves be governed by this fundamental moral principle.
The gay community's embrace of the principle of marriage I believe is a perfect illustration of what Peter was talking about when he said "purifying their hearts by faith."
(And, for what it's worth... I don't see much evidence that mandatory celibacy is a "yoke" members of the Church are willing or "able to bear" -- though straight members seem willing enough to "tempt God" and "put [it] on the neck of [gay] disciples.")
I think the sign of whether same-sex marriages fulfill the law of chastity is whether we have the Spirit poured out on us in consequence of contracting and honoring our marriages. And I'm seeing an abundance of evidence that we do. So it's up to the Church now to figure out what to do with that evidence of the Spirit in our lives -- just as the Church had to contend with the signs of God's favor toward the Gentiles at the Council of Jerusalem.