What weaknesses are responsible for Brutus' downfall?

He displays several weaknesses throughout the play. One of which is his inability to distinguish his thoughts and opinions from that of the group. He refuses to remain loyal to his friend (Caesar) because the majority of the Senate says that it is right. How many examples do you have to give and do you need citations from the text? How long should it be? and for the love of all that is good don't quote me directly the teacher will search for plagiarism.