Hmmm. That must have been upsetting news. How did you handle it?
It's probably best that it came out, though. That way K didn't have a "sword to hold over H's head." But even if K is a "bad guy," he is (was?) still H's husband and had to be respected in that sense. Honesty and consent are necessary ingredients to make polyamory work. So, at the very least, H and K needed to come to some kind of a decision about whether they were going to stay married to each other (and if so, under what conditions).
K doesn't sound like the kind of guy who would accept a polyamorous situation, but I'll await the next installment of your story to find out what happens.
Love means never having to say, "Put down that meat cleaver!"