Yes! My Stepbrother Sucks

Ilana transfers in and on her first day sees a tall swimmer across the campus and takes him for the ex-boyfriend who cheated on her. She walks up and starts on him, and while she is doing it she catches him in the middle of something with an assistant coach. He is not her ex. He is Paxton, the star of the swim team. She goes home that evening to her mother's new husband's house and finds Paxton there, because her mother's remarriage has made him her stepbrother, and his family is rich. They now live under the same roof, share meals with the same parents, and have to explain nothing about the scene on the lawn to anybody. Neither of them can stand the other at first, which does not last, and whatever is between them has to be kept out of sight of two parents who have just married.