Regulus' news was heart breaking, but the brothers had never talked after what happened to Juli. They didn't feel the need to.
Therefore, the second time Sirius felt loss as deep as that of Juli was when he cradled baby Harry in his arms, trying not to look at James and Lily lying on the floor.
He should have understood it when Peter didn't get a letter. When he didn't participate in a lot of missions or when he didn't address Voldemort by his name. He shouldn't have wasted time blaming Remus.
He would make Peter pay for it and truth be told, he did his best, but the traitor had done what he always did. Ran away and killed 13 innocent muggles in the process.
Sirius had to rot in Azkaban and pay for crimes he didn't commit. But the only thing which kept him going was that he didn't betray his best friend. That his Godson was still out there and so was Pettigrew.
The second time Sirius felt panic the way he had when Juliette had disappeared to fight Mulciber was when he got to know that Harry had gone to the Department of Mysteries. For him. This was maybe even worse. Harry was all that he had left.
When he saw his unwillingness to kill Pettigrew, he saw Lily's kindness in him. When he saw his willingness to join the order, he saw James' and Juli's determination in him.
And when he saw him fight just like his father, he couldn't help but say, "Nice one, James!"
He would protect his Godson at any cost. Or die trying.
As he slipped through the veil, he tried to say sorry to Harry and to Remus. But no words came out.
So he closed his eyes and thought of Juli and Starla. And James and Lily. And how they would finally be together again.