confusion between kieran, cas, and poppy

guys i am so confused.

currently through my reading process of figuring out the dynamic between the three characters; are they a throuple?,

or mostly open?

i can’t tell because i know that kieran and poppy are emotionally involved, and knowing that cas and poppy are mates of the heart or something like that. but in general i’m just really confused. are they all dating or does poppy choose between the two?