
Well I kind of get it. After loosing his wife, his self confidence wouldn’t be very high compared to the guy he likes, who he does think highly of and would see as someone people would target. Maybe he thought the blackmail was going to be to keep away from him. It’s hard to think correctly in moments of stress and panic, like being exposed to having a relationship with your student.

Why are you comparing whose done worst? If they both sexually harass and blackmail him they are equally as bad. The person is right he is stupid. Your getting sexually harass and partially exploited and instead of going to the police you start to date the one who did all that to you and trust someone who is so obviously not a good person? I’m sorry but he’s stupid and. Beyond help. All three of them are bad characters
There is a clear difference between being "naive" and "stupid".