My agent is definitely polyamorous.
Your agent would get along with plenty of my characters, then.
People generally ask that question when it comes to gay marriage in general, although in real life I think there's certainly a large number of social/tax/economical issues that are relevant.
Depending on where you are, I guess. There are a lot of laws regarding de facto partners that are the same for same sex couples in Australia now.
I think in the context of the game, they just like to have people make meaningful choices, and not be able to marry every companion and NPC. What are the odds that every romanceable companion in the game is totally cool with sharing?
I don't know many polyamorous people who are totally
cool with sharing either. Sharing with rules and negotiations, and with coping mechanisms for jealousy spikes, sure - but those things don't need to be represented in-game. If polyamory were put in SWTOR (which I don't expect to ever happen) those things would be non-mechanical writing elements, I assume.
Then again I don't know a single polyamorous person who's not in some way or another a recovering monogamist living in a monogamy-centric society. Historical evidence suggests that people brought up in societies accepting of non-monogamy don't (surprise surprise) have hang-ups about it.