How do you get rid of addictive behaviors?

I'm 27 and I quit nicotine after 5 years, about 5 months ago. However, since then, I've been overeating trying to fill some kind of chemical deficiency in my brain. I don't feel like I know what to replace it with, that's the problem. I have a hard time motivating myself, and it took me 9 years to graduate college, which I just did.
How do you get rid of addictive behaviors?
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