Your friend may be depressed, or he may just be bored. Perhaps he's hanging out with the wrong people. Since you said he likes these things, you probably can't stop him.

Be honest and tell him like it is...share your feeling like you have here and he may perk up. This would be especially helpful if he is depressed. How long has he been doing this? It sound like it's a recent thing so maybe sharing your friendship and caring attitude will have an impact.

He's not proud of his behavior since he's asking you not to tell anyone; hence, it's probably something he'll be relieved to quit, given the right advice and support. Tell him how much you care about his health and how worried you are. If all of this doesn't help and he's not willing to seek professional help, tell whomever you must, especially if you believe he is depressed or may become suicidal. These things will only make him feel worse in the long run. It's tough being in your shoes. Tread lightly but be strong. That's what good friends do. Don't be afraid he'll hate you for stepping in - he will thank you in the end!