Is the father responsible for his son's sexual deviance, and is his estrangement from his son considered a severing of kinship ties?

The answer to your question, which includes two matters: your responsibility before God for your son's deviance, and severing ties with him, is summarized as follows:

Firstly: Parents must raise their children well; as Allah Almighty says: ﴿O YOU WHO HAVE BELIEVED, PROTECT YOURSELVES AND YOUR FAMILIES FROM A FIRE WHOSE FUEL IS PEOPLE AND STONES﴾ [At-Tahrim: 6], and as the Prophet, peace and blessings be upon him, said: (Each of you is a shepherd, and each of you is responsible for his flock). Your residence in the lands of the disbelievers increases this responsibility, therefore, residing there is prohibited. If there has been a shortcoming, you must repent and seek forgiveness, and work to resolve the current problem and prevent its recurrence.

Secondly: Do not boycott your son or expel him from the home. His presence with you provides greater opportunities to try and reform him through direct and indirect means, such as accompanying him to Islamic centers or places that help in his repentance. You must remind him of Allah and instill fear of His punishment in him. Be close to him and accompany him in shared faith-based programs, such as reading the Quran and the Prophetic biography, and an Umrah trip. Make sure to move to an area where greater opportunities are available to help in his recovery. The door of hope is still open, so try to influence him with heroic and manly stories, and occupy him with activities that benefit him physically and materially, such as physical sports or part-time jobs. And before all of that, always supplicate to Allah to cure him and guide him back to truth and righteousness.