"I trust you to want the best. I'm just worried what you'd do to get to that best." And, also, what Severus thought the best was. Sometimes he wasn't sure. He knew James didn't lie and James had told him some things. Sirius hated being stuck between two friends. "I'm just worried. I know that dark magic is tempting. It's powerful and all. But--"

He really wished he was better at putting this into words. "It's not a tool. I think eventually, it always makes the wielder into the tool."