"We'll help look after him," James said. Making Remuses happy wasn't solely the responsibility of their Sirius, even if they were in love with their Sirius. It was James's job to look out for him as well, and for Sirius. He hadn't realized that this particular Moony was unhappy, but he was going to do something about that, if he could.
But first, he wanted this Sirius to feel better. He was a mess; James had been able to see it before he went for the hug, but the way that Sirius hugged him back told him even more about how he was feeling. He had always communicated with and reassured his best mate through physical contact, and that seemed universal across the worlds. It was vaguely funny to be on the other side of this hug-- to be the version of a person that someone was missing terribly, rather than the one doing the missing. But not really so very funny, when it meant that there were multiple worlds in which he and Sirius were missing each other.
"It's alright, Sirius," he said, curling one hand into Sirius's hair. "I forgive you." He didn't know exactly what Sirius was apologizing for-- probably something to do with James's death in their world, since that was the kind of thing that a Sirius would carry horrible guilt over-- but he didn't need to know. He had forgiven his own Sirius for everything he'd been through, and no matter how bad that had gotten, James still believed that there wasn't a damn thing he couldn't forgive Sirius for. He didn't think there was any James who couldn't forgive Sirius for whatever it was he'd done-- at least, not any James that loved a Sirius, and the James of this world obviously had.