Understandably "Euphoria" fans exploded online when Rue drops the bombshell question, "How long have you been f****** Nate Jacobs?" to Cassie in front of Maddy and several other characters. However, what really got people in an uproar was that Cassie, after telling Nate she was crazier than Maddy, immediately denied it and backed down in fear.
Cassie first flees from an enraged Maddy, still denying what happened, then says the transgression was okay because Nate and Maddy were on a break. As u/curiousbarbosa wrote on a "Euphoria" subreddit post though, this is "a pathetic excuse to avoid consequence."
Rather than confront what happened and repair her friendship with Maddy, Cassie lies and then denies that Maddy even has a reason to be angry. One commenter noticed that while Maddy can be cruel and vindictive in general, Cassie "felt bad for doing s**** things but she still continued to do them."
Cassie is obviously more dysfunctional than a truly awful person, but it's also not surprising that Maddy calls her a "coward" when she won't even face up to how she's hurt her best friend. Viewers will have to watch Season 3 to see if Cassie will atone for seeing Nate or double down on her bad behavior.