Their "drifting apart" doesn't sound at all plausible to me after the events of "The Ties that Bind".

And Bertie marrying Bobbie? Did he forget that Bertie came to view that prospect with horror? And that she was happily engaged to his friend Kipper?

(As for the whole Lord Yaxley thing, everybody takes it as a given that Bertie will inherit the title, but how can we be sure that it's not just a life peerage? Is there something I'm missing?)