I am going to go a different way! Maybe because I am an addict. I was doing stuff for 6 years and lying to my wife about things. She never suspected it was pills though..Until I told her myself.
If you love him give him at least a chance. I don't think anyone should walk right out (if you love him that is)
We addicts do need help and if we are willing to change (as I did) we need your help as well. Some of us cannot do it on our own.
I would take the "are you doing drugs" way. Tell him you are willing to help but ONLY and ONLY if he is going to clean his act up!! And he only gets one chance!
Dont throw away something you have or had if he is willing to change!
Again this is only if you love him and think the relationship is worth saving!!