"Both the duty of loving one's neighbor and the sinfulness of homosexual activity (or indeed any sex outside of marriage) are part and parcel of the deposit of faith, taught in both Scripture and Tradition from the apostolic times."
I have never seen such a scripture.
And what does one do with this scripture?
2 Corinthians 6:14
Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?
So, I guess love of neighbor has nothing to do with Christianity or Christ's teachings? As for the quote from Corinthians, obviously the apostle Paul tells us that it's probably not always a good idea to hang out with those who are unrepentantly carrying on with evil. However, that does not mean that we should not love them by praying for them and, if appropriate, upbraiding sinful behavior.