Did I unintentionally sign up for a three-some?

I just started Crown of Gilded Bones. I am a spoiler queen and already know about what happens during the joining. I am not a fan of any poly relationships of any kind and am wondering if I should DNF. Especially a series that is heavy on “mates”. A poly relationship definitely just pisses all over that and makes it irrelevant. If it’s a one time thing, I can just scrub it from my brain and ignore it, but if Kieran becomes this constant third wheel or it becomes a FMM I would like to see myself the door immediately.