annon. i just read your reply, and my advice still stands. One of two things occured with your situation:
people got involved in a consensual affair (not you but the others, you say there was just attraction, but no affair with you), which is really none of anyone's business -or-
the sensei picked up on vernuable women and took advantage of it, although he seems to be sticking by his last affair like he cares about it.
women who are vulnerable can be targeted. But you cannot run around trying to protect them from the world ('though some may want that very result). You need to get them into counselling so they stop being the kind of person who attracts predators. Looking back with wiser eyes i see a lteral feeding frenzy of predators that appeared after my divorce; luckily good friends and a wonderful therapist taught me to avoid them. Without them, i would have undoubtedly been snatched right up by the next predator. but now it doesn't matter how many or how strong they are, i can identify them, and hopefully am less attractive to them.
it is a lot harder to change the predators, even more difficult to rid the entire world of them. The best defense against them is to change the behavior of their prey.