His reasons for killing Caesar seem to be strictly personal.

A. No, it was during the play, he thought Brutus shouldn't have killed Caesar.

Brutus appears of killing Caesar by bathing naked in a river and from then on seems less worried about his actions.

As a result, he felt obligated to kill Caesar in order to preserve the republic.

The senators kill Caesar and then stumble out on the streets of Rome.

"We have to grab Brutus before he can kill Caesar."

"Is that remote enough to consider joining a group of men dedicated to killing Caesar?"

What better way to kill Caesar than out in the open?

That way, no one will ever know whose dagger actually killed Caesar.

He is, therefore, not involved in the plot to kill Caesar.