I think, he would only have told me, that I shall not trust in B, that he would hurt ma feelings. In fact, some of the Sempai DID warn me several times, but I didn't listen.
Sensei (the other Sensei) even told me:"B has the potential of a killer, he is a danger, mostly for himself, but also for others. Not on the mat - not at all, but off the mat. I don't want to have this potential of aggression in this dojo. That man is going to get shot out there, if he does not change !"
I bolded the last part of your statement for emphasis. So let me get this straight
Your sensei already KNEW about slimeball's "dangerous" tendencies - and yet ALLOWED him to train? Which not just put YOU in danger, but also the rest of the female students? It doesn't matter if the other students have spouses or are otherwise "taken". A sexual predator does NOT care about such details. What he did to you was a CRIME; has he ever been reported to the police? And WHY is your sensei even allowing him to continue training at that dojo...completely scott-free?
You need to decide for yourself if the relationships you built is worth the lack of safety you currently feel - and your sensei's apparent lack of empathy.