Benson always cuts to the heart of it w/ his words.
I'm not quite so succinct, but let me share:
I don't understand the concept behind homosexuality, nor do I understand how someone can know God and then walk away...
But I, like Paul, often realize I don't understand why "I do the things I don't want to and don't do the things I should", either.
My prayers are for you to find strength to love your Son unconditionally where he is right now and leave your own pain at the foot of the cross.
Something dramatic has occurred in your son's life to turn from God's Son. Something----retribution, judgement, rejection...something.
His only hope might be to find unconditional love from those whom he looks to most.
Not condoing love, but unconditional love.
Having said that, I don't know if I could either, but I sense it needs be said.
Prayers for your own strength and discernment and God's HOly Spirit to empower you to do what on your own, is impossible
... and prayers for your son to have a Road to Damascus experience FROM GOD, so that he might know his Heavenly Father's power and might.
Keep the Son in your eyes!