In Episode 7, we see Jimmy at the Army hospital, and just when it seems like he's going to seek help, he and Harrow leave. Why does Jimmy refuse to take the test?
He realizes that the test isn't meant to help him. It's to find out how to make better soldiers.
How has the war changed Jimmy?
It's changed him completely. He no longer trusts the government. This war was the first time soldiers were going up against machine guns and chemical warfare. The soldiers had no idea what to expect. He comes back capable of doing inconceivable things because of what he's seen in the war.
What does he see in Harrow? And why does he decide to use him?
He sees in Harrow someone else who understands what the war was like. Someone else whose life has been shaped by it. And Harrow's also highly capable. Jimmy's starting to build a crew for himself.
Before meeting Harrow, Jimmy was taken with Pearl, a similarly wounded soul...
I think Jimmy sees a little of himself in them. He feels wounded. He's drawn to these people and wants to help them in the ways that he can.
Does Jimmy consider Capone a mentor? A friend?
He sees Capone as an accomplice. Yes, they're friendly and have a bond. He even goes to his house and meets his family. But Jimmy recognizes that Capone is too much a loose cannon to get too close to.