I would suggest to him that he is probably mistaken. If he persisted in that pathology, I would advise him to seek professional help. If he refused and elected to wallow in his perversion, I would inform him in no uncertain terms that I would continue to love him, but that that part of his life was not welcome under my roof.
“I would suggest to him that he is probably mistaken. If he persisted in that pathology, I would advise him to seek professional help. If he refused and elected to wallow in his perversion, I would inform him in no uncertain terms that I would continue to love him, but that that part of his life was not welcome under my roof.”
I’d also add that you need to educate him about the expected consequences of his homosexual behavior.