Hi there
Is there any way whatsoever that you can get some kind of drug test soon to prove to him that you have stayed sober? stick to your story because it is the TRUTH! Liars always change their stories all the time so you stay honest and stick to the truth and keep reminding him that you have been honest. You have had drug tests which showed you are clean so that should satisfy him.
I know this might sound a little crazy or even a bit silly but heck if it came down to it maybe a lie detector test!