I think you are getting to the root of things. Your friend whose house you stayed at sounds really seriously mentally disturbed. If this is the first you are noticing this, then it sounds like you may not have known her too well.

Your boyfriend may be wondering about how much insight you have into people. To be brought to stay at the home of a stranger, who then attacks you for no reason, is an awful experience. Yet you handled it appropriately by going to a B and B. I think he has had his confidence in your judgement about people shaken. That's a bit unfair over one incident, but it sounds like this was very upsetting for him.

You described the trip as having gone really well, and then you mention this incident, as though you hadn't thought of it before. Maybe you have a tendency to gloss over things that need to be thought more deeply about. I have a feeling that's what your boyfriend thinks, but he's not going to verbalize it to you. Try asking him, specifically, if he feels you let him down by bringing him around this female friend. It may have left him wondering what other disturbing people you may introduce into his life. I'm not trying to be hard on you. You seem to have done all you could to correct the situation. But I think you'll find that this is what is on his mind. He has had horrible turmoil and trauma in his life. He does not want to be led into the kind of situation you described. It wasn't your fault, and that is why he is not saying much about it to you. Still, at some level, I suspect he feels let down that he was led into this by you. You didn't mean it to happen, but it did. You obviously do not know this girl very well. But you thought you did. Not your fault, but you do need to become more perceptive about people. This is what I believe he is thinking. Check it out. I could be all wrong.