Well, there is a physical aspect about cannabis. Consumption of cannabis causes the body temperature to drop about 0.5°C average. If you have consumed cannabis constantly and stop abruptly you will feel like having a light fever for a couple of days. This comes along with light sweating on multiple occasions, because the body got used to the lowered temperature and has to adopt to the new temperature then.
In general, I separate drugging people into 2 types:
- Type A takes drugs and will eventually end up with mental problems.
- Type B got mental problems and is thus taking drugs.
Type A often ends up taking drugs because of outer influences: unemployment, boredom, loss of loved ones, 'bad friends' etc. Once the crisis causing influences vanish, type A might be able to stop drugging and is able to continue a normal life if the drugs have not caused mental distortions.
Type B has mental problems and thus does not feel one with society, or is having a hard time to integrate itself into society. Type B usually develops an affinity to drugs, given the feeling of being able to stabilze its mind in a situation which would be otherwise dragging the mind down. If you take away one drug from type B, it will find others to abuse.
If that girl is type B, your claim for drug abstinence will only drive her away. Instead of sharing things, she'll have secrets then. If you are not type B, type B isn't for you either.
I guess one of the few possible constellations where a type B can stop drugging would be a strong master-slave relationship in which type B focusses on the partner as a substitute for the drug. I'm not sure whether that is an option for you.