I’m 18 weeks in and desperately want to smoke right now. Need some encouragement beyond just to keep going

I experience major depression along with my addiction and the depression has been giving me massive cognitive decline. I can barely remember what I ate the day before. I quit weed for thinking it was the cause of the sharp decline in cognitive function, however now at 18 weeks I have felt practically no change. Really itching to smoke, what can convince me not to. Perhaps going even longer I can regain some clarity and memory along with brain function?