I actually was in a similar situation as you...

What I did was, I just kept my grades up, got a few scholarships, went to college, held a job, and never mentioned anything about weed. My mom knows because I've come home smelling like smoke a few times, but she hasn't ever pushed the subject.

I'll admit, this has led to us talking less. But that's what happens if your parents don't want to be understanding; you move away from them.