Hello Clear, it is difficult when your partner is addicted to whatever, and in your case, he has a drug addiction, and you are right, he has to want to go to rehab, otherwise, it's a waste of time.
If he has tried to quit, that's great, but it's not easy, so can I suggest he visit his doctor, be honest with them and ask them about some medication that will stop the urge or want to use drugs.
This is also used for people wanting to stop drinking alcohol, it works on the same principle because it stops any urge to use, I can't mention the name for BB rules but if you google what I have highlighted you will find out the name.
There are different types that can be taken, but for me, only the strongest was good enough to stop drinking, his doctor can explain these to him.
When you want to stop then no alcohol and/or drugs should be in the house and if any is hidden away then the person has to be honest and hand them over, so no temptation is possible.
Supporting him like what you are doing is definitely a bonus for him and he will thank you.
Another suggestion is the people he frequently visited needs to also stop, as the possibility of them saying to him 'just have one, it won't hurt you' is a temptation no one wanting to give up wants to hear.
Please let me know if you have any other questions.