Was it ever a sin to be gay? This question cannot be adequately addressed by denying there is such a thing as sinfulness altogether, for there are billions of people for whom the hermeneutic of sin is an important aspect of their understanding of life. This kind of outright denial is like trying to persuade a bank to let you off a debt by convincing them that money is just a fiction: you may be right, but you certainly won’t convince the bank.
Kierkegaard suggested that sin could be understood as despair, the “sickness unto death” that can only be conquered by faith, specifically faith in oneself. He saw this despair as originating in an intensified weakness or defiance; a failure to be what one knew one truly was, a hopeless longing to be what one is not, or a denial of one’s true nature. Sin for Kierkegaard was the heightening of despair, and this is a reading he was able to develop well within conventional Christian doctrine. He particularly noted the verse in Romans (14:23) which says “whatsoever is not of faith, is sin” and thus observed that the opposite of sin is not virtue, but faith. Faith in oneself was the antidote for despair and – for Kierkegaard and any other theist – faith in oneself had to be anchored in God, or at least in one's idea of God.
(I personally find a gainful parallel in Kierkegaard’s account with the Dharmic concept of karma and karmic burden, but this is not the time to pursue this thread).
What I find particularly interesting in connection with the question being asked here is that on a reading of sin that follows Kierkegaard being gay was sinful, at least for many people whose sexuality was of this nature from the mid-twentieth century backwards through history until at least ancient Greece. Being gay for all but a precious few in those sadly restrictive times inevitably meant either denying one’s true nature or despairing of expressing it – gay meant being in despair, which for Kierkegaard is sin. It’s easy for us, looking back, to rage against the circumstances that caused this suffering, but it doesn’t change the despair that gay people living in these times had to endure.
But now the dignity of homosexuality has been renewed and with this has come the possibility of two lovers of the same gender declaring their love publically, and committing to a loving bond on the strength of their faith in each other. Faith, according to Kierkegaard, is the one cure to despair, and the very opposite of sin. And as long as gay lovers have faith in each other, then their love cannot be sin.