He’s definitely addicted! But once he creates the monster, don’t you think his response is a bit unlike a normal addict, in that his feelings aren’t mixed at all? I’m just amazed how quickly he hates his creation! That said, I agree that his relief at being free of his creation is a bit like someone who has just kicked the habit.
I’d love to find some more biographical criticism that touches on your observation. Did Shelley have much exposure to drugs/addiction?