"dope fiend" does not mean a pothead. Weed is only called dope by those who have never done any drugs, and a fiend is someone hopelessly addicted to a substance so much that they would suck a strangers dick for it.
its a comparison to how much a person can love another. The love is like an addiction, and it becomes necessary to that person.
"Dope fiend, dope fiend I'm just like a dope fiend
When it comes to your love
Girl I'm like a junky
Dedicated to your drug
Baby let me get some Smoke you, snort you, shoot you in my system"
-johnta austin