Hey man I don't think you fucked up at all. When I was a gradstudent in my mid 20s I had several friends who were still underaged who pressured me to buy them booze. A few times I did it thinking "well, they are almost 21" or "what the hell someone else will buy it for them if I don't." One time I remember telling a couple of them "Don't you guys drink this damn stuff and get behind the wheel" and one of them sarcasticly responded "Yes Daddy."
Then one weekend there was a horrible car crash a couple miles from campus caused by a drunk 18 year old kid who tried to pass on a couble yellow. The driver of the car he hit head on at 70 mph was one of my best buds who was the designated driver for a bunch of his friends who had been to a party. My buddy died at the scene, as did the guy in the passenger seat. The 18 year old driver of the other car died instantly but somehow the passenger in his Camero miraculously walked away without a scratch. My bud's roomates who were in the back seat of his car survived but they were all badly injured and hospitalized for weeks.
A few days later this friend of mine (from church of all places) that I had bought beer for in the past came by my apartment with a list of what he wanted from the beer cooler at the supermarket and asked if I could "hook him up." I said "No, I can't" He said "Dude that is so uncool, WTF is the matter with you." I just completely lost it and started sobbing, I picked up the newspaper with my buddy's obituary (and his picture) that was lying on the table and handed it to him and said, "Here is what is wrong with me dude, he was one of my best friends and now he is dead because some guy who was driving drunk killed him. Don't ever ask me to buy you beer again, and if you find someone else to buy it for you, STAY THE FUCK OFF THE ROAD!"
He said "OMG I heard about that crash, I am so sorry man". Then he tried to change the subject by asking "so what have you got going on this weekend? I said "I am going to his visitation tonight and his funeral tomorrow." He stood there silently for a few minutes and then he said quietly "Hey man I would like to go with you if thats cool." As we walked out of the funeral home tears were streaming down his face and he didn't even know the guy. I suspect that the sight of that handsome young guy lying in a casket dead, and his parents who were completely inconsolable at the loss of their only child is something that will be with him as long as he lives. I know it will be for me.
Someone supplied the alcohol to that teenage kid, more than likely it was one of his friends or family members. The cops were unable to find out where he got the booze but I am sure the person that bought it for him knows, and they will have to live with that for the rest of their life. If that person has any conscience at all, knowing that they are responsible for getting him and two other people killed is probably much worse than anything the criminal justice system could do to them. I honestly am not sure I could live with that...I would probably commit suicide.