He is an adult, this is his issue to resolve, not yours. Your actions do not make him use.
Honestly, he has made no progress, again 2 months clean out of 6 is not recovery, and what you are calling relapses, is not reality. He is not in recovery, and if you are not in recovery, you cannot relapse.
It is your decision to hang on and pray for a miracle, or move on.
You are codependent, are you attending Alanon or Naranon meetings? Have you read Codependent No More? If not, I would suggest that you do both.