I had a similar thing going with my exabf who drank...and the drinking eventually led to full scale relapse and the coke turned him into a jerk. Sheesh, compared to drugs the drinking didn't seem all that bad, but you know, he never went off and did stupid things when he was sober, drinking was always the first step to stealing or drugs or irresponsibility.
basically, any one in the field knows -- addicts just can not do any drugs of anysort, they even have to be careful with prescribed things.