Well, there's a theory I feel could be highly possible:
- what if the concubine is just acting under the orders of Gong huanyu, and what if gong huanyu is a spy from wufeng or maybe a pawn of wufeng spy.
- what if the wufeng spy has somehow got gong huanyu under his/her control ( not by blackmail but by other means like brainwash something) and has been nurturing gong huanyu to destroy the gong family.
- what the concubine is actually a good person who has been brainwashed by gong huanyu saying that ' he is doing this for the better future of gong family.'
- if the director uses complicated mind, I have a feeling the concubine would be a mere pawn in the game, who isn't really aware of main deals behind.
Or you know it is also possible that gong huanyu's mother is wufeng spy, who has been brainwashing him against gong and for wufeng. Afterall we don't know who gonghuanyu's mother is yet, I mean it's not shown yet.