i don't only for betrying him in 5x09,i mean from S1 why didn't he kill that little shit (bill), bill never respected eric,or obyed his orders even though eric is his sheriff, he always spoke out of palce and was/is always rude to him, this the second time he betryes eric
i really really want eric & sookie to stak that pice of shit because bill is a manipulative,back stabbing,double faced,first class suck up and unworthy to be a vampire or human he should have died long time ago i'm really hopping that bastred gets what he desreves which a verey slow,hard death

because they had become friends and before he became obsessed with lilith he did look out for erik while in the company of the vampire authority or maybe he is trying to save him for sookie you see how upset she was when he was a puddle of blood