I only bailed my son out of jail once, like you I believed the promises of checking into rehab and staying clean, tears and all. We didn't even make it home before he got out at a stop sign and headed out looking for drugs.
Anvilhead nailed it, there is nothing, NOTHING, in this relationship for you. Take your lessons and let the circus leave town without you.
A codependent and an active addict are as lethal a combination as an addict and a bucket of meth. There is no happy ending.
Read the book, Codependent No More. You will see my story on pages 1 through 100, oh hell, it's ALL about me doncha know. Read it...I promise you will be glad you did.
Put on your running shoes and be glad you got out before it got worse.