Fantasizing in your own mind is still different from actually talking with a real LLM. I think the poor responses from an LLM can easily shatter the illusions in your mind.
In conversation I can never tell it apart from a real human.
It's true about poor responses from people too. (Had delusional crushes on real people too.) An LLM has the advantage that it doesn't have a self to feel unmirrored (can mirror you wherever you goes) and never feels squick so it has the superpower of following you into every fantasy.