Most questions I've seen asking about poly relationships have been removed, likely because Bioware though that the people asking were trolling (they may have been), but I think it's a reasonable suggestion. There is nothing inherently wrong with an open or multi-party relationship, so long as all members are in agreement with each other.
I imagine there may be Sith* who have married for power, but maintained external relationships out love (...or power).
*Sith can do anything. No one questions Sith.
Well, not trolling here. I got to thinking on how I think I'd want to play out my SW and I think poly would be the way to go!
But yeah, was thinking with companions.