Poor K. She's just so jealous about J and Motley Crue and she just isn't doing a good job at all hiding it. She wants to be all anti-guy and anti-sex like A but she just doesn't have it in her. She's always been desperate for men and committment and it's not a habit you can kick in a day.
It's not like J is one of those obsessive girlfriends. Seeing Motley once a week is more than enough. She refuses to call him her boyfriend and says she just doesn't want to put a label on it which probably means she refuses to be exclusive. She won't introduce him to her family no matter how many hints she drops. She only answers about one in every five of his calls and never calls him. She doesn't even talk about him that much, except if he's directly related to the conversation or someone asks about him.
But K has a problem with the whole relationship. She has a problem with the fact that it's J in the relationship. She acts nice to J's face but then turns around and bitches about it. She's been complaining to A for weeks that all J ever talks about is her new boyfriend, which isn't even true. She's perfectly sweet to Motely but then she makes snide remarks to J about how he's job/looks/personality aren't so great. She makes a face at B every time she hears his name or anything related to him.
Then again, maybe she has reason to be paranoid. Remember secret admirer and accidental date? Why couldn't she have gotten rid of them instead?