My bf tested positive for meth. he's been clean for over a year. they are sending to lab. will the lab determine if he tested positive because he was around meth being smoked or if he was actually the one smoking meth?

Yes, a person with second-hand meth smoking can be tested positive with heavy exposure and urine was tested a short time afterward. When test is (+) it's difficult to say due to exposure or active use. To me, the chance of relapse in that environment is much higher than a true second-hand meth smoking & I doubt if any authority will accept the (+) result due to second-hand exposure.

A lab test only determines the presence of a chemical in urine, not how it got there. You and your friend need to find different friends.