I just made my dad relapse.. He caught me with a bowl and weed. He's been clean for 25+ years. Now he don't wanna stop. When he smokes, he doesn't wanna stop, he will smoke all day long. I'm afraid something bad is going to happen like government splits us up..
Talk to him about it! If he refuses to stop at least ask him to tone down a bit and only like smoke on the weekends, and since you also smoke weed smoke it with him! It can be a great bonding experience!
Damn... 25+ years? Find the best solution man.
You can't be blaming yourself, you did not make him do anything.
You need to try talking to him, and if that doesn't work get help. Find someone both you and him trust, you should hae to do this alone.