Please read up in the books suggested on this site for what you are going to face and go through. He may very well be going through withdrawels. Good luck as you make your journey one day at a time. You might find great support there with his drug addiction. Also, i-village has a great support board for addiction recovery.
People grow through experience if they meet life honestly and courageously.
I don't think the method of the discovery is all that important. The important thing is the attitude after the affair comes out. I do wish that my husband had ended it and then confessed, but that wasn't the case. What has made the difference for us is that he has been totally committed to me and our marriage and to healing from the beginning. He showed remorse and repentance and turned himself inside out to win back my trust and help me heal.