disclosure is a good way to build trust and you did manage to control yourself and that's why you got onto Methadone - it's often seen as the responsible thing to do.
if you choose to use a bit here and there, so be it - it's your passion and reward (that's how i see it).
as long as other facets of your life aren't suffering, no need to feel guilty.
... you never know where friendships will take you so as long as you are sincere and wish to slowly release information about yourself, you're doing right by the both of you.