I'm guessing...and this is just a guess...Nathan said he didn't feel welcome in the house (that's why he left)...I knew he singled out when he left Tim, Drew, Tahan (I think he wrote stuff later on FB about her saying a lot of mean stuff that wasn't on TV...whatever.).but he probably just didn't get to know them and mistook their actions for bullying..
I think Tim tried to get arguments out of people to make them look bad on TV (but that's the game...I wouldn't call that bullying)
and Nathan's a quitter so who cares about him anyway...he should've gotten the Justynn treatment and not been invited to the finale..instead he got this stupid applause as a great guy for sacrificing himself when really he's just a quitter.