If you and your son are already on unsteady terms, I wouldnt try to persuade him not to go. That will make him want to do it just to spite you. Trust me, I am twenty years old and while I am a grown-up I still feel the need to defy my mother at times. Take a step back, and let him know you'll be there always (or you can tell him not to come crying to you whenever they take all his money, whichever stance you may take lol), and let it go at that. He may fall down but at least it will teach him a leson. I have learned lessons the hard way and while it sucked, I am still glad that I did it and learned on my own. It is so much more meaningful to learn things yourself! I am sure you raised good kids- but thats what they are, just kids. Big kids, but still kids
Everything will work out.