Is it obligatory to provide for a son who commits fornication and openly declares it, or to assist him when he is in need? And what is the ruling on visiting him and eating from his food?

Adultery is a grave sin, and publicizing it is an even greater offense. Part of publicizing it is for a servant to uncover the veil Allah has placed over him. Al-Hafiz Ibn Hajar narrated from Ibn Battal that publicizing a sin is a form of disrespect towards Allah, His Messenger, and the believers, and that concealing it ensures safety from such disrespect. It is obligatory to advise the son who commits adultery, to instill fear in him, to remind him of Allah, to involve someone whose words he respects to influence him, and to supplicate for his guidance. It is permissible to visit him and eat from his food if there is hope that this will have a positive effect on him. There is no harm in shunning him if doing so serves a benefit and does not increase his obstinacy. As for financial support for an adult son, the majority of jurists hold that it is not obligatory. It is permissible to give him money as long as it is not known that he will use it for unlawful purposes.