Colleen, Your story sounds so similar to mine. "only" using Pot (and then drinking on occasion). My son too, is in college, but when he is home, he lives exactly the way yours does (mine is turning 21 very soon, which makes me even more concerned). Because of some recent issues, I have told my son that he cannot live at home this summer when he is on break. I just can't have the behavior and issues here any longer, as I have two other sons who have to see and hear it (18 and 12). I have no idea what he will do for the summer, but I had to recently tell him that my days of enabling him (trying to help him solve his problems) are over, and he is on his own. It's going to be so hard. But please know, you are not alone! It is helpful to me to hear from others here with so much experience. It's also helpful to hear that I am not alone in how I feel- I completely share your "Facebook" issues- it's that time of year again, and though my son is in college finally, it's no where near what it "should have been", but I have recently learned to just accept that.
Hang in there!