Philippa's error is to give of herself too generously. The man she gives herself to as wife proves disastrously unequal to the passion she lavishes on him.
He feels stifled by it, and after only three years of marriage his thoughts tun to the idea of escape - and his eyes elsewhere. 'Elsewhere' means an attractively self-possessed young woman who is Philippa's 'best friend'.
Philippa's odyssey is long and painful before she can finally come to terms with her abundant nature...