Just to reiterate a fine point: homosexuality per se isn't a sin. It is a disorder, like caries or depression or alcoholism or being born with a cleft palate or foetal alcohol syndrome. There cannot be a moral judgment (eg ascribing sinfulness or fault or blame) about a disorder as such - some arise from disordered actions (eg addiction to opiates) and some arise through the quirks of life in a post-lapsarian world. Many homosexuals report a complete involution in their condition. Reason and charity require that we accept that as true.
Those actions (thoughts, words, deeds, or their omissions when there is a duty to act) which fall within the ambit of the human will are either virtuous or vicious according to the degree of the matter and the volition of their agent.
Also, temptation is not sin. Christ was tempted and yet without sin.
I might be born with a strong temptation to indiscriminate copulation with members of the opposite sex, and adultery is sometimes a very strong temptation. But these proclivities don't make such actions necessary. Hard to deal with, sure. But not necessary. We are much more than our proclivities and desires. It's how we act on them that is morally significant.