What I am reading is that he wants to do it "his" way....with your $$. His way is probably going to end in death.
Your way could (and probably will) end in death.
Codependents have an unhealthy sense of "being responsible" for.....well.....everything.
With all of the compassion in my heart I would tell you that he is not your responsibility. Even tho your heart (and his manipulation) is tricking you into thinking so.
With all of the compassion in my heart I would tell you to save yourself and give him to his higher power. If his HP wants him to get help....it's not going to happen with you "in the way".