I'm going to assume a different "favor he will never forget" from what current teachers will do for a boy.
She made me a crossing guard sergeant, and always showed me kindness, as she showed kindness to all the other children in her classroom. When a 23 year old teacher has an affair with a 15 year old boy she is merely gratifying her own perverse appetites and not doing anyone a favor.
When I ran into her at a book fair in my senior year in college and mentioned the prestigious engineering school I would be attending in the fall, she reached across the table full of books and gave me a peck on the cheek, if that satisfies your prurient curiosity.