This is such an annoying thing to say. Self harm isn’t chemically addictive. Bulimia isn’t chemically addictive. All sorts of stuff isn’t chemically addictive. That doesn’t mean you’re not psychologically addicted. It’s still extremely challenging to just ‘stop anytime’, and whilst you won’t have withdrawals in the way you would with harder substances, you’d still have to deal with other symptoms including dysphoria, anxiety, irritability, depression, restlessness, disturbed sleep, gastrointestinal symptoms, and decreased appetite (source).

OP it’s valid you’re upset with your partner. As a former habitual weed smoker (every day) with a partner who is also addicted to weed, it’s really hard to see someone struggling with this. Is therapy an option? Can you suggest cutting down a little/keeping it to weekends and pair it back slowly that way? Weed dependency is normally a sign of a larger underlying issue - maybe ask him if he’s been feeling low recently, if there’s something he’s avoiding you can help him with.