Euuck. I feel for the wife too.
Re affairs with teachers and pupils, I never get this. I'm probably too naiive but even if there is an attraction, I don't know why you'd risk your job, family hurt, and whole career in teaching, not forgetting the abuse to the pupil. This never happened at any schools I went to, that I got to hear about. It did happen at uni. I think lecturer (guessing early 30s), and student (19) is fine. It still created lots of gossip, but no loss of job. They are now married with two children.
A friend trained as a geography teacher, and moved to a new town for first teaching job. He was about 23 at the time. On his second day in new job, he noticed the pretty girl he'd snogged in a nightclub, a fortnight earlier, was a sixth form student. Fortunately not taking geography a-level.
Apparently she clearly recognised him too, but amazingly never bragged (that he got to hear about). He wasn't sure whether he should admit it to department head, in case there was an issue later on, or keep quiet. He went for the latter. It caused a lot of jibes, as he confided in one friend, who naturally told everyone else. He never went to a nightclub, in this town again, for fear of sixth form students. He didn't like the familiarity.
If this friend had got together with sixth former, after she'd finished her a-levels, then this would have been fine, but he had the common sense to know to keep away from her, when he was a teacher.