Hi Cat C and welcome to the forum.
Your post above rang a loud bell with me. It was almost my story with my son, you know, the story is the same but the details are just a little different.
yet we found out he was skipping school and drinking only after he left
Yes, that is the way it is. You likely don't know much at all about what is really going on. If he is drinking...or using any kind of substance, that can explain all of it. Every single bit of it. A person who is living under the influence is not a person who is going to act in any kind of rational or reasonable way...the way we understand life to be. And all of your tears and words and other reactions will not change it. I know because I tried them all.
I think you are already doing remarkably well. It took me a long long long long long time to truly understand that the only person I can change is myself and the very best and highest love I could offer my son was to get out of the way and allow him to deal with the very real consequences of his own very real choices. That is the only way he can decide if he likes his life or not, his life without all of my safety nets, and then get motivated to change.
Only when we are completely and utterly sick and tired of our lives are we motivated to change. That is a truth I have learned over time. Them and us.
We do not give him money and we finally told him if he wants to sleep at our home, he needs to get up in the morning and leave when we all do.
This is an excellent boundary. It's not all or nothing. Then...they can choose. And if they choose "nothing" then they have to leave. This is a very reasonable thing to require. That is my test of my idea of a boundary---is it reasonable? Does it work for me? It's my home, and I get to decide if an able-bodied person is going to lay in bed most of the day, stay up most of the night, not work, use substances, play video games all the time, leave dirty dishes around all day, not help at all around the house...on and on. I get to decide this, as this is my home. And so, this boundary is about me, and not about him. But by setting it, and by deciding what works for me (not a "I'm going to teach you a lesson, and I'll show you, and I'm mad") then he gets a chance to experience the very real choices he is making, the natural consequences, and then he can decide whether to stay or go. When a boundary comes from what we want and need (and is not all about THEM), and is reasonable, then it has a good chance to be a solid boundary. That is what our DCs truly need, someone who is willing to set good boundaries with them.
Then...they have a true chance. That is what we need to seek---giving them a true chance to live life on life's terms and experience the consequences of their choices, whether that is lying on a bench in a park, high as a kite, all day and all night, going to jail, being homeless...whatever they are.
I thought I would die when my own precious son was right where your son is, and so I truly understand your feelings here. Our feelings about the children we love so very very much are the toughest part, because what we have to ultimately do is to defy our feelings and go with our new ways of thinking and behaving...even while we are still having these very strong and powerful and instinctive feelings.
I also had to "Play the movie" about the phone call you mentioned. I had to finally accept that anything can happen to anybody at anytime and I can't prevent it. I can't prevent my older parents from dying, from falling on the floor and lying there because they refuse to move out of their home and get the help they need. I can't prevent my older son from dealing with the challenges and hurts of learning to live in a new marriage, and I can't prevent my oldest friend from the grief of losing her husband slowly from an incurable disease. I can't save my own son from his addiction and from himself. These are hard truths for people like me to learn, people like me who have been very good fixers and managers and controllers and who just want the best for people, right? We have the best intentions.
Please take very good care of yourself right now, and do small kindnesses for yourself, much like a good friend would do for another. This is very hard stuff to live with. I believe it's the hardest of our lives.
Please keep sharing here. Others will come along with words of support and encouragement and ideas. Take what you like and leave the rest, always. We are here for you.