This makes me wonder if the holidays are really hard on our older sons. Since S21 and your S18 are both struggling right now and they have the same kind of temperament and way of lashing out to handle their emotions, I am convinced it is somewhat due to their fathers not living at home during this previously totally family oriented time of the year.
Just a thought.
Everything happens for a reason, maybe Dad needs to find that it isn't better out there, he needs to realize how good he had it here. Maybe he will find God and that is the most important thing when he finds Him he will know he is supposed to come home.