I mean, I mostly thought Carlyle's problem (having only read these bits out of context) was that he depended rather too slavishly on Wilhelmine as a source without thinking that she might have had her own (psychological) agendas.

I agree that was a major reason. I think a secondary reason is that as Fritz got older, he started making more life choices that she couldn't agree with, and it was a lot easier to blame the people he was hanging out with than to blame him for his own bad judgment, or accept that they were starting to have different values and priorities.

I agree with both of these -- I definitely got both of those vibes from Wilhelmine. (Though to be honest if I hadn't had context provided by you guys, I'd probably have been just like Carlyle and taken her at her word.)