I have tried to encourage them to be cordial. He doesn't care that it might be painful, hurting her, or even humiliating to her. From where I'm standing, it's like being asked to back out of a commitment because of his feelings. She has feelings. I don't know if it's anger that's making him say to bloody hell with her or if that's how it's going to be from here on out.
He hates the notion that Si's part of our marriage. His whole argument is, "I didn't marry her. I married you. If I had married her, I would have included her in the original vows. I know I didn't." I get it. It blows him. I view her as an equal, and he views her as some random person who isn't worthy of that anymore. He's doing his best to cut her out. Now, it's just not a secret, and the intentions are being spelled out before they happen.
This elephant isn't going to break down.