Drug Abuse Help (Significant Other)...?

I have been with my boyfriend for about a year and a half. Before we met he was into drugs. Mainly coke back then, from what he tells me. Then he moved onto prescription pain meds. He had pretty much quit doing them all together when we got together. Then after about 4 or 5 months one of his "friends" at work gave him something. I knew something was up then because straws were disappearing from the cups in his room. I flat out asked him and he told me the truth. That was about a year or so ago now and he hadn't done anything since up until recently. He started carpooling with some of his co-workers (different job than before.) I got suspicious because I could just "feel" that something wasn't right. At first I though he may have been cheating but then I asked him if he was snorting again and he admitted it. He says that he does one pill a day, max. Mostly Perc 5s.It bother's me so much that he is doing this but I don't know why or what to do? I can't tell that he's doing them because he doesn't act any different but just knowing that he is drives me nuts. I don't know why? Maybe because my mom died of an overdose (health complications got her addicted.) I don't know how to make him stop?! Just some insight would be nice... I don't have anyone to talk to about it because I'm ashamed and my family would tell me to leave him but we have a home together that we have worked hard for. I love him so much and I just want to help him. Do you think he will "grow out" of it? Note that we are only in our early 20's. Someone just please tell me something to ease my mind...