Which government? This isn't Federal, it's local. Fornication at any age is wrong and destructive of the community. And if I were the girl's father, the dude would know what destruction means. If she has a father at home. Hitting on students is criminal. A school district would be insane not to eject teachers for extra-marital misbehavior of any kind, because of the example of students as targets for adults' exploitation, or promoting disrespect for marriage.
Yes they would also be insane (and many are) to put up with teachers notoriously committing adultery. Without respect for marriage, civil society collapses. And in case we've forgotten, a school is a place where people put their kids in loco parentis, specifically because they trust they will be educated with selfless care and respect. If you want to start a career like the Marquis de Sade, fishing for action at the local high school will get you shot. With good reason.
ANY government. I don't disagree with your viewpoint, but understand no law was broken...that was my point. I didn't catch that the man was married, but obviously I don't condone that either. I also pointed out that the school probably has a policy to enforce, as it should.