Aww I'm sorry lovely, but gently, you need to remove yourself from this situation.
You cannot help people who don't believe they have a problem and, don't want to change.
And you are not his therapist, his addiction sponsor or, his mummy.
It's only two months. And tbh when people use the word 'intense' to define new relationships...it's rarely a good thing. So that worried me before you even talked about the drugs.
I don't know if you meant it in a good way TBFas you don't mention things like having being love bombed etc. But...whirlwinds usually either blow out or...blow up everything. So they're usually a red flag.
I know it's hard to find nice men but, if the roles were reversed and you had a drug problem, you'd attempt to deal with it before dating right? Because you'd recognise it wasn't anyone else's problem to fix. But he's just plowed on, got involved with someone and is now dragging her down...making her sad... That's not nice.
Please choose yourself and your own happiness and peace. No joy can come from trying to fix an addict. Let alone one who doesn't want fixed.
He may change his tune when you tell him why it's over. But, wish him well, do not continue to date him. Addicts must quit for themselves. Otherwise every time they fall of the wagon it'll be 'i never wanted to quit anyway, I just did it to stop you nagging'.
Hopefully he will get his shit together. But he needs to do so elsewhere. You need to do self work too, work on protecting yourself from bad choices like him. And towards choices that protect you. I know you know what needs doing. Sometimes the right choices are sad. But maybe do him good in the long run. And it'll do you good indefinitely. Addicts do not make kind partners. And the bare minimum a partner should be is kind.
Let him go.