My partner's sibling and him had a conversation once his affair came to light and stated that she wasn't surprised that one of us was unfaithful. For me, I know this is not something that I would be able to do. It feels as though she is transferring some of her own guilt and shame from her own infidelity, but it has given my unfaithful partner leverage to use against me and transfer his own shame and guilt of his affair. They come from a household of divorce due to their mother having an affair. Their families unspoken moto is them against the world and has been a huge issue in our entire 17 year relationship. He seems to always choose her side and I have always felt second place. It feels as if they are all placing blame on me for my unfaithful's bad choices. This makes me feel that she has the window into our relationship and I have the wall, the outsider. How to I confront this and be able to move forward?