“It seems that before she got involved with him, your problems could have been solved with better communication and perhaps couple’s therapy (to deal with the misunderstandings and possible resentments here and there). But once he started exerting his influence, she flipped.”

Just like I said before, once he influenced her, she threw the towel and blamed it all on me, before that she was willing. He himself voiced that he tried to make her break up with me.

“There was probably some unresolved anger in her, maybe anger at her brother which she falsely directed at you.”

Actually I don’t think that’s the case. What I noticed is that she started to mirror his behavior towards me and using the same tactics which were alien to her before.

“How are you feeling about it now?”

I’m not sure how to feel but things have been (very slowly) getting easier. For now I’m giving it plenty of time and not contacting her.
I still can’t shake off the feeling that this development has been very wrong and there’s some sort of childish hope growing in me. I want to believe that she’ll have to fortitude to come back to herself and detach himself from him, so we can at the very least have a proper conversation like we used to.