How much time has passed between the end of act 3 and the opening of act 4? In that time span between acts 3 and 4, what events occurred in ancient Rome?

 Almost two years pass between acts 3 and 4. In the two years after Caesar's death, Mark Antony, Lepidus, and Octavius formed the Second Triumvirate. They also recruited an army that would take on Brutus and Cassius' army.

Crusoe believes that money is like a drug for several reasons. Before the shipwreck, Crusoe does not seem to be motivated by any force outside of himself. He is not close to his family, and seems almots incapable of deep feelings. Moreover, his qualities, although admirable, are always directed towards his personal success and individual accomplishments, one of this being making a fortune. Although Crusoe claims not to care much about money, he is constantly driven by the pursuit of it. In this way, Crusoe is like an addict, and money is like a drug.