^The sad part is Duncan lived a lie, not the sexuality, but, this betrayal in the end casts a black curtain over the entire marriage. If she'll do this, then what else has she done, how else has she forsaken him and their bond? I'm confident they sat down in the beginning and discussed the different facets that Duncan's sexuality would entail. There was full disclosure. A full sex life was probably something that she could sacrifice for a life with him. I'm sure she was in love with him. Sex & love are at extreme ends of a long line. Most every woman's goal is to be a mother. He agreed to that and provided his essence.
People change. But, that is an excuse, not a reason. She changed from a girl--to a woman-to a woman of self actualization. And there was the break. She was presented with a choice for the second time in her relationship with Duncan. Unfortunately she was bound for life with the first choice and her first decision. And now she's sold her soul with the second.
Only a ing animal would do what she has done.