The kiss was never brought up.
Winter thinks that it's for the better. With everything that's going on, she doubts that getting into a relationship is a good idea. Not only does she have so much to deal with, but she also can't afford to get distracted by her feelings. She admits that she's a coward for not confronting the truth, but being blissfully ignorant is preferable sometimes.
Marcellus probably understands. The reason why he never talked about the kiss might be because he doesn't want to pressure her. He's giving her all the time she needs to sort out her thoughts and emotions. Besides, he knows that she's more than aware of how he sees her. So, he's also not oblivious to the fact that she's not ready to enter a relationship yet.
That's one of the things that Winter has come to like about Marcellus.
