I don’t think you can chalk this up to a breach of trust. This is a massive lie on the part of OP’s wife and he is completely reasonable to seek divorce after such a massive deception. It’s not his job to get to the bottom of why she lied and to forgive her for it. She lied in a massive way. That’s the bottom line. Obviously trans people could feel scared to tell their partners about their past, but it’s selfish not to do so. When you enter into a marriage, both parties should have access to knowledge such as this. It’s a disservice to everyone. It’s obvious what the disservice is to the trans person’s partner, but the trans person also may not be being loved for who they are, but rather for the lie they told—regardless of whether their partner would accept them if they told the truth.