This is a slihtly different version of a previous idea i posted. Before the female teacher was much younger, 16 i believe. I was thinking of a story where a young woman of the age of 20 is a teacher at a high school. One day she finds that she is falling for one of her male students. She stops herself from pursuing a relationship with him 1 because he's 17 and 2 because student teacher relationships are frowned upon. So she finds herself a boyfriend. It's nothing serious but for a while it keeps her distracted from the male student. Then soon after he turns 18 her feelings for her student get stronger. The one day she is unable to fight the feelings they both have for one another. They have sex. And they even do it at school. But the principal catches them. He tries to blackmail her into having sexwith him. He thrates to tell her boyfriend. But she is saved by her younger sister. Her younger sister is 18 and reveals she has always had a crush on the principal and she offers her body to the principal to save her sister. It works. The principal had liked the younger sister for a long time but couldn't find the oportunity to do anything with her. Once the female teacher becomes pregnant from her student she feels it's time to break up with her boyfriend. That or he breaks up with her because he can't have kids or they never had sex. Shortly after graduation she marries her male student.
