Needpeace, you are not responsible for his using or not. I hope that therapy can help you accept that. This kind of emotional blackmail services neither of you. All it does is make his recovery dependent on you, and therefore his relapses will be as well. And they are not. His recovery or lack thereof is entirely his responsibility.
Sometimes loving someone means letting go so they can find their own way, even if that way isn't the way we would choose for them. Sometimes it means not having them in our lives because the relationship is unhealthy for both of you.
It's not about turning off your emotions so much as it is about accepting that he is an adult and fully capable to taking care of himself if he chooses to.