Answer:
He killed Caesar because he was worried Caesar will demolish the republic and it was for the good of Rome. Julius Caesar also planned to claim the title of king, overthrow the Senate and rule as a tyrant, were the principal motives for his assassination. If that didn't help read the explanation.
Step-by-step explanation:
Some didn't want to see republic destroyed by one man
Brutus was proud to be a descendent of the Brutus who expelled Tarquin the Proud
Conspirators wanted power
Conspirators wanted freedom to gain power
Collapse of Triumvirate made Caesar vulnerable