My Tutor

The movie opens with scenes of an aerobics class juxtaposed with a classroom of students taking an examination. The movie's two protagonists are featured in these scenes, with Terry Green (Caren Kaye) participating in the aerobics and Bobby Chrystal (Matt Lattanzi) taking, not very well it turns out, his last high school final, in French.
At first, Bobby's main goal for the summer before college appears to be losing his virginity, if not with his unrequited high school crush, Bonnie (Amber Denyse Austin) who dates a college student, then with any takers. Soon, though, the poor results of the French final are in, and Bobby must take a make-up examination and score at least 85% in order to retain his acceptance at his wealthy lawyer father's alma mater, Yale University. Mr. Chrystal (Kevin McCarthy) hires Terry, a skilled French tutor, to live in the Chrystal home during the summer and work with Bobby on passing his exam. In addition to her normal compensation, Mr. Chrystal offers to give Terry a bonus payment of $10,000 should Bobby pass.
Terry and Bobby begin working together but Bobby's lack of interest in both French and Yale soon become apparent. His real goal is to attend UCLA and study astronomy. Terry is sympathetic but reminds Bobby that wherever he ends up going to college, he will need to pass his French final. With Terry's help, Bobby begins to make some progress.
At night, after she thinks everyone in the Chrystal home is asleep, Terry uses the family's pool to skinny dip. However, Bobby sees her one night and begins watching her regularly (especially as his group of friends fail several attempts to lose their virginity). After one such evening, Bobby follows Terry back to her room, only to have her sneak up behind him and surprise him. Terry gently admonishes Bobby for spying on her but it is clear that they have a mutual attraction. After yet another evening out with his friends, Bobby returns home to find an upset Terry, who had earlier discovered her on-and-off-again boyfriend cheating on her. Terry later heads to the pool for her regular swim. She finds Bobby waiting for her and she pulls him into the pool with her and the two begin a love affair.
The summer's end approaches and Bobby has to take his French examination. Despite Terry's attempts to keep their relationship casual, Bobby has developed serious feelings for Terry and resists her insistence that the affair end once he takes his exam. Matters worsen when Mr. Chrystal, who himself lusts for Terry, sees his son and Terry kissing one night. After Bobby successfully passes the test with a score of 91%, Mr. Chrystal reveals to Bobby his promise to pay Terry the $10,000 bonus, implying that Terry's affection for Bobby was driven by greed. Bobby reacts by angrily confronting his father in regards to his overbearing ways and tells him that he will be attending UCLA to study astronomy and now that he is an adult he will no longer allow him to dominate every aspect of his life anymore. He proceeds to storm out to find Terry. He confronts her with the information, calling her a hooker and flees after Terry angrily denies the accusation.
Later, Bobby seeks out Bonnie, his old crush, and, using his new-found confidence with women, is able to persuade her to begin dating him. Terry prepares to leave the Chrystal home and Bobby approaches her to say good-bye. He begins by apologizing to her for his rash accusations and then telling her that he will never forget her. Terry tells him matter-of-factly that she will never forget him. The two share one last kiss, and Terry drives off. Bobby leaps into the air, looking forward to the rest of his life.

Question: Why is Terry upset when Bobby find her?
Answer: Her boyfriend is cheating