My friend recently started doing cocaine-wise to shun him?

A couple of weeks ago, a friend of mine joked that he had started doing crack. When I asked him if he was serious, he laughed it off and told me he was just kidding, but then said that he had really tried it, but only a few times, and later admitted that he was doing it almost every day. Last week, he missed work on Monday, and showed up late on Tuesday, so another friend and I went to go check on him in his dorm room, but he wasn't there, so naturally we were quite concerned. When we got back to work, he just happened to be there. I asked him what had happened to him, and he said he was hung over from drinking and "a little bit" of crack, not to mention a ton of sex (he is a sex addict btw, and maybe somewhat addicted to pot as well). Would it be a wise thing to cut ties with him? I already tried confronting him about these addictions of his, but he usually just turns it around and insults me. I'm not really offended by it, but I get the feeling that I'm just wasting my time. My girlfriend of nearly two years also recently started drinking and smoking pot with her best friend and her best friend's brothers. At first I was ok with it, but still very uncomfortable. A couple of months later, she went and got her first tattoo. I went with her to the tattoo parlor for emotional support, but I still wasn't comfortable with, as much as I tried and claimed to be. I mostly saw it as a manifestation of unnecessarily wild behavior. As a student pilot, I know that these sorts of people would be a severe liability to me once I go professional. Obviously the most rational thing to do would be to sever ties, but I'd like to think I'm not so coldhearted. At the moment, they're just too much of a burden to continue carrying. My friend and girlfriend arent stupid people either, although their decisions and behavior suggest otherwise. Any advice for solutions would be appreciated.