To me, Kendall wasn't upset that Leo kissed Chelsea. It was that everyone knew but her or rather Leo didn't think it was worthwhile mentioning. I'm sure if he approached to her and said like, I'm open to pursuing something else with someone else, so keep doing what you're doing with Joe, she can't really be mad at that (though she was talking about how since there are limited days left, she wanted to figure it out sooner). Yes, everyone is kissing everyone but Colton and Chris knew about each other, Jordan and Benoit knew about each other, Jubilee and Caroline knew about each other. Leo and Joe knew about each other. Everyone at least gives that respect.
Also I mean, it was like 30 min after they got back from their date so that is also weird, but nonetheless.
Leo is a manipulative jackass and at least its good to see this season the women calling men out (Tia with Chris) on that. Like, they think they can convince them of something that didn't happen? These men are crazy.