in Diana Wynne Jones' books come in several versions. There are some who are permanent or semi-permanent partners to the girls or women concerned and those who are more like infatuations - often because the girl/women is under some kind of influence. (See Boyfriend Spoilers
for examples of both types.)
Seb is Polly?'s boyfriend for much of Fire And Hemlock. He is similar to the boyfriend in [Time Of The Ghost]?.