Personifying an addiction can be helpful to breaking it off, as with this sample goodbye letter to cigarettes.
It's time for this horrible power play to stop. I never thought I'd be the kind of person to end up in an abusive relationship, but from the very first day you've done nothing but take away the best things from me and leave me dependent and weak.
I know you think I still need you, that I'll come crawling back, and that I'll keep hurting myself just to have you. That used to be true about me. But I've finally started to realize the way that you've been killing me slowly, chipping away at my health and my nerves, even while you pretended to soothe and steady me.
It sickens me how long it's taken for me to say goodbye, but I'm saying it now: I don't need you anymore. And I won't be contacting you again.