There are multiple issues with this, including very clear moral, ethical, and as mentioned in the article, legal ones.
Regardless of one's opinion on the morality of pre-marital sex, the teacher in this case was allegedly married, and apparently decided to commit adultery at least twice, which should be well outside of everyone's definition of acceptable moral behavior.
Secondly, students are subordinate to teachers, and K12 teachers in particular have a responsibility to act professionally and model good character and behavior for all students. Sex aside, the teacher allegedly also provided alcohol to persons under the legal drinking age, which is also against the law.
You guys who think you're masters of machismo by dismissing or even lauding these types of things need to zip up your pants and engage your brains. It's this kind of moral confusion, poor judgment, and lack of character being modeled by adults that causes all kinds of societal decay. If morals are relative and obeying certain laws is optional, pretty much anything can be rationalized. We can perhaps debate some of the charges and the quality of the laws as they are written, but no one should be questioning the apparent lack of good judgment employed by the teacher in this case.
JKG