If your son is legally an adult now, and does not live with you, there is nothing you can really do besides put the bug in his ear that he needs to straighten up, and even then he is not likely to listen. Kids have to stick their hands in the fire to know it's hot. Let him learn his lessons himself. THAT will make them stick.
I feel your pain. I have one like that, and after many years he's finally completely coming around. I don't have any advice really except sometimes, waiting it out works.
We all thought parenting toddlers was hard - that was easy. ;D
Ugh, rough stuff. I'm sorry going away to college has been such a downward spiral for your son.
Thing is, he's now an adult. You can't manage him like you did when he was 13. This is HIS first opportunity on his own and he's a flop at it. You did your very best I'm sure when parenting him. I know that I've been reading a lot about helping our kids get to the point of being independent adults and it starts before they ARE adults by letting the learn life lessons. If in high school they don't do their home work, they fail. You have to let them fail to learn. Same goes for college.
that is really difficult. I personally would no longer fund his education if you are doing so. Kids that pay for their own education are much more vested in doing well. They understand the dollar and cents of wasting this money and kind of 'get' that they are working for their future. Kids that have parents who pay often do not get this lesson. We have a rental house that is a college property and I tell you, the kids that pay part or all of their expenses are much more responsible.
So, consider this as part of the deal--- he keeps his grades up or he has to find another way to pay for college via loans or what have you.
I do TOTALLY understand the fear that he may drop out and derail his future. I really get that fear.
But I don't know what else you can do.
Would he consider coming home and going to a local college and living at home?