Difficult Situation With A Close Friend

I would just like to say that I have lurked in the Psychology forum for some time as I view it's application to Poker as an investment. I also plan on finishing my undergraduate studies and moving on to get a Masters or Phd to become a Psychologist. Nonetheless, I thoroughly enjoy the open discussion in the forum and decided I need your guys' advice on a very tough subject. Well here goes....

I have this friend, I'll call him Mark. He used to be best friends with myself and another dude I'll call Ben. We all graduated high school in 2003 and have all since gone on to college at the great ole U of A in Tucson, AZ. Ben and I have stayed on more or less the "right track." We both are in school, working hard, getting good grades, and partying only when we can. Moderate drinking goes on, during the weekends, as with almost all college kids and we stay away from drugs because we both feel, for us, they only sidetrack us from where we eventually want to be.

Mark on the other hand has not stayed away from excessive partying, or the drugs, and he has dropped out of school this semester. He has no job and is living off of his dad's money. Here is the thing. During our senior year of high school Mark's mom died of cancer. To me, it has seemed, ever since that event Mark has never been the same. This all leads me to the drug abuse that I am extremely worried about. It's mostly marijuana, every day, 5-6 times a day. I have not seen one of my best friends not high in maybe a year. He also drinks 3-4 nights a week and I have seen him take mushrooms before also. As a result of all this he has gained 60+ lbs. since high school and as I said before dropped out of school. He does not talk to Ben and I nearly as much anymore, he hangs out with younger kids, some of whom are still in high school. When he does talk to Ben and I he can't remember things and it seems he just doesn't care about much of anything. I am worried about his health and well being as I have seen one of my best friends make some horrible decisions with his life.

Ben and I have talked about confronting him on many occasions but we just don't know how to do it. He is very guarded when it comes to the subject of his mom but I have a feeling all of this leads back to the death of his mom and him not knowing how to deal with it and cope.

Any advice you guys have would be much appreciated as myself and Ben feel like we wouldn't be his friend if we didn't say something soon. Thanks.

Clark