You've made a mistake like any human being. He will have to get over this. How unrealistic is it to expect that you should be perfect and never make mistakes.
Let him know that you did not tell him because you felt afraid, ashamed and anxious in regard to his response. You must of felt disappointed in your relapse as well.
Ask him if he would be willing to help you quit (it takes time and effort) and show him that being supportive is more helpful to you than angry.