Sirius hadn't had the chance to grieve like this for James and Lily - he'd immediately gone after Peter and once he'd been brought in he was half mad with the loss of his friends and knowing that Peter was still out there. But here now it was all catching up to him.
He shook his head closing his eyes tightly trying to stop the tears, but even that wasn't enough. "I don't know what to do anymore." He confessed, because he could be there with James as long as he was alive, help him with the potions and get a hold of Stephen as many times as he needed - but in the end there wasn't anything he could do for him.
And that was what was the hardest for him - with James and Lily at least it had felt like there was something he could do, he could go after the person who had been responsible, but now ... there wasn't anyone to go after, not without getting himself killed as well.