Sirius would never forgive himself for doubting Remus for even a second. For trusting Peter over him, he'd had those same thoughts that James was having now for years now. "You're going to have to get in line if you want to do that," Sirius told him shaking his head, feeling tired and old, and aching for his friend, and at the same time just so overwhelmingly pleased to see him that he didn't know how to contain it. "I tried." He told him, "After -" He couldn't say it. "I hunted him down, I was going to kill him, expose him for what he'd done and kill him. But he - he transformed before I could do anything."
There was so much James needed to know and Sirius didn't know how he was supposed to tell him everything, not when he'd just been facing down his own death. "Look at me," Sirius said reaching out, putting his hands on James' shoulders and making him look only at him and nothing else, focusing him on this. "Harry survived." He told him, "I found him that night." His voice cracked, still remembering how horrible it had been, hearing Harry's cries and everything else so quiet. "He couldn't kill Harry."
As for this place, how they got here. "It's some sort of magic." He told James helplessly, "This place picks people from different worlds and brings them here. I don't know why or how. I've only been here a few days myself it's been... I don't know maybe five years for me since the time you've come from." Maybe it had been more, maybe less, he wasn't sure. "There's magic here, but no one seems to know how it works."