I want to say that I have seen something similar to this in my own family and what follows is just my reading of the situation.
Orion is addicted to a toxic substance, i.e. a manipulative girlfriend! I saw it happen with my brother a long time ago and it ended quite badly... eventually. No matter what you say, no matter what you do, Orion will not respond well or act like someone who is thinking rationally. That is the hallmark of an addict and the drug is sex.
Of course, I could be completely wrong about that and I hope I am.
I'm going to somewhat disagree here to say that Orion himself is responsible for his own behaviour, and that addictions to substances and/or relationships aren't the primary issue here, and need not be considered for handling the primary issue, which is about the right of people to set boundaries in their own homes and the right of potential visitors to come or stay away depending on how they feel about those boundaries.
Speculation on secondary issues and other parties tends to shift the responsibility away from where it belongs, and make "excuses" for poor behaviour.
I'm mentioning this because I'm from a family where I saw my mother for many years blame my brother's bad behaviour towards others on his wife, and her alleged sexual hold over him. The responsibility for an adult's behaviour lies with the adult, not with their spouse, or with addictive substances.