The official stance of The Church of Jesus Christ of Latter-Day Saints on homosexuality is:
The experience of same-sex attraction is a complex reality for many people. The attraction itself is not a sin, but acting on it is. Even though individuals do not choose to have such attractions, they do choose how to respond to them. With love and understanding, the Church reaches out to all God’s children, including our gay and lesbian brothers and sisters.
The LDS church is in support of basic civil rights being extended to those who self identify as homosexuals. These rights include equal access to housing, medical care, employment and the like. They are not however in favour of homosexuals joining in marriage or gay cohabitation. This reflects their stance of, "People may not choose who they're attracted to, but they do choose how to act on those attractions."
Recently, because of the supreme court ruling which made gay marriage legal in the USA, in addition to the other countries in which gay marriage was previously legal, the LDS church found it necessary to update their definition of Apostasy to include same-sex cohabitation. Prior to the legalization of same-sex marriages, it was not necessary to be so specific, but in order to address the secular position that homosexual unions should be held in the same regard as traditional unions, the necessity has arisen.
Amongst other questions, in order to receive a temple recommend, an individual must honestly be able to answer in the negative to the following question:
Do you support, affiliate with, or agree with any group or individual whose teachings or practices are contrary to or oppose those accepted by the Church of Jesus Christ of Latter-day Saints?
Supporters of those gay rights which directly affect the definition of the institution of the family, specifically, those who support the institution of marriage between homosexuals, the cohabitation of homosexuals, or the adoption or raising of children by homosexual couples, are literally in support of practices that are contrary to the teachings of the church. They are literally in support of apostate teachings and practices.
Does this updated policy mean that all supporters within the church who believe that gay individuals have the right to live in gay relationships are guilty of apostasy?