One who is so in love with a particular person or thing in the same way that a drug addict is in love with his/her hard drugs.
It was used by daveedope, a Nigerian Hip Hop artiste who raps and sings in his debut track. It's even the title of the track.
When it comes to Lily, nigga forget it I'm a junkie for love.
It is when two drug addicts (junkies) are in love with each other.
Sharon is comforting Bob who is smacking out at the train station, awwwww junkie love.