I would say that he's a jerk for doing this just because she broke up with him... but it is also very much the rules for when a teacher and student start dating. Maybe expulsion for the student is less normal, but that is also assuming students who haven't forced the entire studentbody to go commando against their will, and flashing her privates to teachers and anyone else watching, to seduce said teacher. So not like he actually had much choice in the end, and he did stay his hand for quite some time after the breakup until she stepped over the line of what he could turn a blind eye to.
Honestly more surprised she didn't end up in legal problems. Even before this arc
But hey, all's well that ends well. Not only did he find a new pantyless loli to groom (this time blonde), but his ex-fiance will also get to become a happy housewife asap, before she's even graduated school! What? What do you mean those are all huge issues? :tehepero: