Which domestic thriller books talk about a secret affair between teacher/younger student with a happy ending for them?

I apologise in advance for the topic, and if it’s inappropriate for the forum I’ll report it to the moderators. I’m looking for the plot in question with the affair described in the title. Then they flee but after a few years things go bad for the friends of said student. While the student returns a little older she reunites with her friends (yes, I prefer a girl than a boy who conducts the affair) and describes she has a happy life. Then… well, open ending but it ends well for the student “in love” (well…) and a bit “rude” for her other friends who have to face reality in stark terms.