He would never conclude or admit that his fairly extreme lifestyle had any negative effects.
I sort of expected this to happen. Several years ago, on one of their summer trips to Canada, they spent some time with her parents. He wrote some highly critical, mocking things about their consumption habits. It's possible she wanted a little less of the frugality and extreme eating habits and the criticism of her family.
His parents divorced many years ago, and that often has an impact on whether the kids divorce. In addition, his father died of an aggressive brain cancer in early 2017 IIRC. The death of a parent often sharpens one's focus on how short life is and changes your priorities. He's a constant optimizer, so a new and more suitable partner might have become the top priority.
It's important not to lose the message in the personal details of the messenger. There are far better examples of successful FIRE-ees that are easier to relate to, but he has influenced a lot of people's mindsets and behavior. By spreading the "gospel," he has accomplished a lot in the FIRE movement.
