Ok, so if the violent stuff was bipolar issues that are now medicated and under control enough so all can feel safe? And you are willing to be in partnership with her and make reasonable allowance for her condition? Ok, then... maybe it's a question of letting go of the triad thing? Could that relieve tensions / unmeetable expectations?
Not just in the (you + H + K) sense. But overall? A model like
Your sweetie (K or not) + (you + H) + H's Sweetie
like an "N" or "double V" thing that might be more realistic/attainable?