It might seem like a romantic ending but it isn't. It was a selfish move on the part of Edwin, Paulinus, Æthelburh, and Breguswith—a move Hild had to accept. It's also the springboard into the next part of the story.
My book club just had a discussion about Hild. It was a lively exchange. I enjoyed the book very much, but several of us had issues with the ending. Our question is why do you have Hild and Cian end up together? It seemed like throughout the book Hild (and everyone else except Cian) knew or guessed that they were half siblings and of the clear taboo that this posed. We didn't want to see the book ending on a typical romantic novel story arc.
What follows contains spoilers for the beginning of Book II so skip everything between the lines if that's something you want to avoid.
- It keeps Cian safe because:
(a) He's no longer regarded as a contender for the throne—he's now officially Ceredig's son, not Hereric's, and therefore not an Yffing and therefore not a rival to any dynasty.
(b) If he's no longer Edwin's chief gesith, he's much less likely to die in any upcoming battle.
- It keeps Hild safe, because she's no longer the seer, no longer linked the king as his political advisor, she's a wife
- If Hild is safe, her gemæcce is safe.