Obsession goes even colder than this.
Rewatch the opening monologue after the ending. It stops sounding like love. "You're in every song I listen to." "I'd choose you over everything." We've heard those exact sentences in a hundred rom-coms, always scored with strings, always rewarded with a kiss in the rain. I think Bear is speaking the language we’ve been taught to recognize as love.
And then the film asks what happens if you actually mean those words. It turns that poetry into behavior. Someone who thinks about you constantly. Someone for whom you're in every song. Someone who would choose you over everything. Even her own self. That person is post-wish Nikki.
She's not a corruption of the romantic ideal. She’s the romantic ideal, performed faithfully. The horror isn't that the wish went wrong. It's that the wish went right. That's the horror.