It's not okay to share roommate sex stories. Everyone has a right to their privacy, and sexual experiences are among the most private aspects of a person's life. Even if the story seems harmless, it can still be embarrassing or disrespectful to the people involved.
In general, roommate sex stories are not appropriate to share without the consent of all parties involved. These are very private and personal matters. Sharing them without permission can violate someone's privacy and make others uncomfortable.