Swimfan (2002) on Netflix

New Jersey high school senior Ben Cronin is a former juvenile delinquent, whose past criminal behavior was fueled by and for drug use. He credits the support of his now long time girlfriend Amy Miller and getting into competitive swimming as the primary reasons for turning his life around, which includes working part-time at the hospital where his single mother works. He has become the star swimmer of his high school team, so much so that scouts from Stanford University are coming in a week's time to watch Ben swim. Ben has a new swim fan in Madison Bell, a recent transfer student to Ben's high school. Despite Ben making it clear that he is in a committed relationship, Madison seduces him, the seduction to which he succumbs. They agree afterward that their encounter was a one-time only event, but Ben slowly comes to the realization that despite Madison's assertions to the contrary, she has more in mind with him. He feels her constant unspoken threats to expose their tryst and ultimately when he rebuffs her totally, unspoken threats to ruin his life in whatever means possible. Ben quickly learns to what extremes Madison is willing to go, especially when he finds out about her past. He has to figure out how to regain his life back from his known stalker, which is aided by the reason Madison is in New Jersey in the first place.