If a person decides to harm themselves there is nothing we can do to stop them. And if he is blaming you for this, he is not accepting responsibility for a very bad decision. If he is active in his addiction, it will be very hard for him to get proper treatment, because a doctor just can't know where the substance ends and the mental disturbance begins.
It's not your fault. Keep telling yourself that until you believe it. If you had any control over this at all, then when you asked him to stop using he would have.
And...I hate to say this, but blaming you is definitely manipulative. "If you don't do what I say/want then I will harm myself" does not put the responsibility on you.
He needs help, I hope he gets it.
Hugs