I often re read the books and I think he was the classic first boyfriend. She wasnt interested in the loud mouth types, so she went for the quiet bookish type. Jack Cavendish was a total arse, no idea what she saw in him!
I found the fact that they gravitated back to each other at times of stress or trial was interesting. And how she put up with him at Oxford....again very questionable!
But I do like the fact that the final book leaves it open that they may actually get back together in its ending.