Yes, on the whole I think Gavin had fairly good reasons for being an arse. (As do many other people - Marthe, for instance.) And frankly, Sybilla's suggestion that if Francis had died Philippa might have ended up marrying Kuzum is skeevy in the extreme, given that Philippa had cared for Kuzum as a baby. Though that would probably not actually be incest, not that Sybilla knows that.