GoodKarma,
He's just doing what addicts do. You mustn't be surprised -- every time you take him back, you make it so he can do this to you (and to himself) again.
The only important question is whether it's how you want to live your life. He has his own journey, you have yours. Do you want to keep supporting him and stay in your front-row seat to the madness of addiction?
Hugs,
GL