Let's put you in Nick's shoes for a second.
The situation with Heather just came out, and now, you're being blamed for things you ACTUALLY didn't do. You'd feel ganged up on, I kind of understand why he just lashed out at everyone like that.
The rest of the bros aren't blameless, everyone should've learnt their lessons from what happened with the Halloween party, and taken five to really look at the situation from the beginning. Instead, people let their feelings take the wheel, and boom, what happened, happened.