Hi there,
Sorry you and your partner are going through this.
In my experience, and that of others on here, the will to change has to come from him. It has to be a genuine desire of his to seek help for his addiction. He will need the support of groups and professionals. It’s so hard to accept that someone has chosen a substance over a relationship but that’s how powerful drugs and alcohol are.
I left my partner about two weeks ago too. He hasn’t even tried to fight it as he’s not ready to make promises he knows he won’t keep or to admit he has an issue.
However you handle this, don’t feel alone. If you can, convince him to get friends and family involved. The less secrets the better. Hiding things and telling lies just makes everything harder. After all, addiction is awful but there’s no shame in it. The same as any other illness.
Take care.