I’m actually not sure if it was in /r/eroticliterature or /r/sexystories, but I got permission to post from EL but not SS, and the search function didnt help me at all, so I’m here.
So the story was in self.posts, not linked to somewhere else, and it was told in the girl’s POV. She lives with her mom, and has a crush on her cousin (I think) who stays with them sometimes.
In the first part, the girl is having period cramps in the living room, and her cousin comes in and gives her a massage, using massage oils iirc. He massages her lower legs first, moving her pajama pants up to go higher. Eventually he ends up fingering her, and the orgasm relieves her of the pain. The chapter ends with no sex.
I forgot how many parts it was, but in the final part, it’s Christmas or some occasion, she, her cousin, and her mom eat dinner together and she gives her cousin a set of scented massage oils (Her mom gives her a weird look) and her cousin gives her a calendar.