Life changing problem. Please don't judge me. I need sound advice from an outside source?

I am 31. I married my husband 12 years ago. All we both wanted was to have a family and for me to be a stay at home mother. I have done that the whole time. I have been a good wife to him. We now have a 4 year old. He is our world. My husband is a good husband and I never would have thought what I found out today. I was looking in his truck for my insurance card and found a little baggie full of drugs. I have never taken drugs in my life but I know that is what it was. My husband never sleeps. Ever. I know now looking back what an idiot I am. I know he has been using. All his friends do and I am just a freaking idiot. I am in dental hygiene school and I am half way finished. I have one more year left and my closest family is 2 hours away. I can't make it by myself without quitting school, and if I do that I am screwed. I have a better chance at finishing. Everything is in his name. Yes again idiot, but it is not like we have anything worth anything. We rent, we have 2 paid off cars that are worth like 5 grand each. I just don't know what to do. Should I stay and finish school. Stick it out until I know I can make enough to care for my son? I don't want anything from him when I leave, so it is bad to say I will stay with him for security until I can live on my own. I can't even believe I am typing this. I don't know what to do. I can't raise my child with a drug Addict. He has lost weight, strung out. I umed it was work, but I have a suspicion it is more. Then where does it go from there? Who is to say he is not cheating on me? I mean he has no problem lying to me about the drugs. I have come so close and so far in my school, and even paid for the $7000 program in advance, so if I quit I will lose it, but I have nobody here. No family. Family would love to help me, but all they can offer is a place to stay 2 hours away. What do I do?