It's more the line between what is a good idea to have fun and share with someone... That backfires a little for the MC when it becomes a bit more than they thought.
Except sharing implies either the GF or Michael are aware of the consent of the MC beforehand - which they explicitly are not, and all signs kinda indicate the interest was there prior to the story - considering she greets him at the door in a towel and blows him within a few hours with no communication to the MC aside from gaslighting and sideways remarks about how well she thanked him.
