I hate Sensei. Such a sleazebag. The scene where they're at the hotel and he says "don't waste my money" and she says "you earned it by tutoring me" was so gross.
Earned money by working for her, groomed her and they had sex, then used the money to go have sex an a hotel. It's like he got a 2 for 1 deal: hotel money AND a girl to go with him.
I don't know if he did anything illegal, but he sure took advantage of a girl who didn't know better.
EDIT: Sensei didn't lie to her per se, and some of what he said was his own philosophy, but to introduce a young, naive person to sex by giving them only that knowledge definitely wrecked havoc on her ability to form relationships.
Meguro had basically no self-esteem: thinking that what she wants doesn't matter, just trying to make her current boyfriend happy. Look at the beginning of the series: she didn't even have any interests or hobbies of her own, or even favorite foods. Until last chapter, she never even got jealous or upset.
Even if he could technically be declared innocent, I think Sensei was a little too enthusiastic about finding a virgin who was clueless but somewhat curious and taking her to love hotels at what? Age 14 or 15?
It's scummy.