Is he a cocaine user?

I've been off and on with my boyfriend now for 9+ years. We were high school sweet hears and eventually got afraid of commitment at such a young age and decided to go our seperate ways. We found eachother again after 3 years of silence and i feel like my situation is tough because he's come back i'm 23 now and he's 25. We're pretty much adults. I get this weird vibe of his mood swings that aren't good. Some days he's the sweetest guy in the world and the next he's angry at the world and annoyed. I know that his bestfriend uses, but i have no way of knowing if he does because he says he does not abuse drugs. How can i tell if he does?! Another thing, he disappears on the weekends and reappears during the week. Is that when he's under the influence of cocaine? FYI, He's not my boyfriend so i can't really confront him. Help!