I think Shadowheart it's okay with an open relationship (hooking up with other people) but not a polyamorous relationship (having relationship with someonelse). We can argue that some thing should be said BEFORE starting a relationship (she is hurt if you hook up with Mizora because you didn't ask her), but I don't think she is written as "poly" because of Halsin. The reason why only with Halsin you can have a sort of poly relationship it's probably because the possible combination among companions were too many. They could have handled it better, but I think they wrote SH as ok with open relationship... because that's who she is, simply enough. But I agree that the player should be able to discuss this with the romanced partner (even just talking with SH and telling her that "You want to be 100% exclusive, no hook up or exception admitted" would be good. She seems okay either way actually).
The writers had no problem in writing strictly monogamous characters (Laezel, Gale, Wyll), if they wanted that for SH they would've done it.
