Sigh-Fi

What about Protagonist bangs his ex-girlfriend but actually it's a cosmic Eldrich monster who's feeding him illusions and when the illusions fracture he sees the monster's true form and is horrified so she wipes his mind and replays the loop so he can bang her again as if it's the first time but it's actually been happening for decades because he's her only living plaything and without him around she may be alone again for hundreds if not thousands of years?