Hina you really should know better, there's no excuse. A kiss here and there is forgivable, but this?
All these hollow characters are just puppets on the author's string. Their personalities are mostly flat. And this triple taboo of student-teacher, adult-teen, stepsister-stepbrother, pfff.
I commend the efforts of the author, because I did enjoy the premise and the first few volumes, however the turn this took just left me sad for the unreached potential.