J already had a chance to take a drunk Kate home, but phoned MC instead. J has also said to both Kate and MC that she will not do anything with them without their partners permission.
The only thing I dislike about J is she will not take no for an answer (and that seems to annoy others as well). Interestingly, Kate says 'the only thing that I didn't like was Michael and his attention on me', but she doesn't complain about J's hints. K and J seem to have a good friendship.
If you talked about a threesome, Kate likes the kiss with J. I assume Kate will then tell MC about the kiss, as she knows you will not be angry, as when she told you that J is trying to get her into bed, 2 of the 3 choices are positive (third is silence).
I hope that once MC knows about the kiss, they can guide Kate towards a threesome. J has no reason to ever mention Michael to Kate again, and hopefully she will realize that she no longer needs to keep dropping hints about what she wants.