Hi Dreams, welcome. I've heard the saying that look within any addict and you find a codependent, and I tend to believe it. I'm really glad your son is doing well...maybe the two of you could try a Naranon or Alanon meeting together?
I know that you are impacted by his choices, but that too is your choice. You may want to think about adjusting your boundaries given this change...Maybe it's time to tell him he has to make other transportation arrangements. I know you want to be supportive, but I know for me, if I feel resentful I can't truly feel supportive.
I'm glad you posted and hope you keep sharing. Hugs and prayers for both of you.