Girl started having sex with her boyfriend 3 weeks ago, hasn't experienced an orgasm yet but lies to her boyfriend about it. After a festival, boyfriend and her have sex and she lies about it again. After boyfriend heads home, classmate who saw them in the act approaches and mentions that she lied about having an orgasm, that she's probably never had one before and asks if she'd like him to show her what it's like.
There's really very little persuasion or anything going on. She pretty much just does it (some mention of rumours among her female classmates about him being good at sex, phone call from her boyfriend where nothing important is really said, then she just goes along with it).
Ends with the guy trying to persuade the girl to fuck again, her thinking she can't betray her boyfriend any further, but then the other guy sends pictures to the boyfriend and that's pretty much it.