Cassidy
I know Sutter was a very dysfunctional jerk, but I'm struggling to have any sympathy for his ex-girlfriend. Her introduction is just her dumping Sutter for being in the same car as another girl. A questionable situation sure, but one she does not give him the chance to explain. She's then immediately moved on to Marcus and clearly sets things up so that Sutter sees them together - all the while she's also sending Sutter mixed signals. The fact that Marcus comes to Sutter for advice on her suggests that she's like that with him as well - and she seems to be a very difficult and somewhat destructive girl to be around.