Addicts know every trick in the book to pass a drug pee test. Unless it was a hair folicle test I would not believe any results. One doesn't just disappear for 3 days for no reason, addicts do.
If you decide to go forward with the marriage, strap on your seat belt, you are in for one heck of a rollercoaster ride.
Read all the stickeys at the top of this forum, lots a great information at your findertips. I would also suggest that you read Codependent No More, it is a good starting point for we enablers of addicts.