Now, I did read the original post and one of my questions to the OP early on was whether she knew that the professor was aware of what her boyfriend had done. I didn't get a response that indicated that the professor definitely knew.
I taught high school through this past school year, and I definitely had students who made it a mission to make my life hell. I've often seen students and former students (who've graduated) in restaurants around town. If I saw a former student and explained to my husband who that student was, my husband would never dump water onto her head and curse her out. Yes, he would be acting of his own accord if he decided to do that, but even if I never asked him to (which of course, I would never do), I couldn't just let that go if I was aware of it. I would apologize profusely to that student because it's so inappropriate. I get that my husband is his own person, but that would never have happened had it not been for what I told him. I couldn't be with someone who I had to apologize for strictly because I would feel the need to apologize for something like that. But, as I mentioned before, we don't know if the professor realized it since the OP did not talk with her about it after that.
One other thing that might be relevant to people's interpretations and responses of the situation (and others who read the original post please correct me if I'm wrong), but I thought the OP was already moving on to another school. Did I read that she was entering a PhD program and wasn't going to have a lot of further interaction with this person? -that the OP was concerned about moving on to a new department in a small, close-knit field where even though she wasn't in the same vicinity, that the influence of this professor could still reach her?
Does that sound familiar to anyone else? It might just be memory reconstruction, but when I read it and was trying to figure out what the appropriate course was, I thought that's what stood out to me as a factor that was considered by the OP.