What should you tell who? The Father? Nothing. The father is telling the truth about going to Hell.
NAd how do you know this? His actions are objectively sinful, but you have no idea what the state of his soul is.
Tell him to keep going to confession and to not give in to despair.
Stir up within Thy Church, we beseech Thee, O Lord, the Spirit with which blessed Josaphat, Thy Martyr and Bishop, was filled, when he laid down his life for his sheep: so that, through his intercession, we too may be moved and strengthen by the same Spir