If SCD had anything to do with it, I suspect it's that Rachel appreciated the new experience and probably wants more. She's an intellectual and probably thrives on challenging herself. Perhaps hubby wasn't on board with that. They got married quite young and whilst back in the day it was normal for people to marry young and still be together today, life is a lot more open now, more to do and less of a struggle to get around and do it. Much easier for couples to drift apart unless they put the work in.
Either way I hope Rachel is okay. I'm not surprised the husband is upset at losing her, she seems lovely.