"I understand," Sirius responded and even though he was smiling through tears, his voice conveyed that he understood that magnitude of what he was saying. He owed James and Remus so much -- even more now -- and he was going to do everything he could to make the last few years up to them. He knew it was probably going to take the rest of his life, but he was committed now.
"I brought a present for Harry," Sirius said, nodding down at the package he had under his arm. "It's from Remus, too. Though, I understand if you don't want me in the house." He tacked the last part on hastily.
It was just difficult to tell where their boundaries would fall now. It was stupid to hope for things to go back to how they had been when they were teenagers. They were drastically different people. Even if they had remained tight friends, their friendship would have changed as they did. As it was, Sirius had to learn the ropes in a way he never had before -- but he would take whatever James was willing to give.