Amazingly, Sirius didn't freeze up. Didn't even hesitate, really, when he found himself with an armful of Remus Lupin. His own arms seemed to remember their place around the other man and find their way there before his mind even registered what was happening. Sirius clutched back almost desperately, feeling for the first time in a year the sort of warmth only Remus could bring him.
Right then, even if just for these few minutes, whatever confusion or pain or unjustified anger he was feeling about Remus's future marriage was completely forgotten, thrown atop a mounting pile of 'issues to be worked out later.' Because right now, all that mattered was knowing this was real, that they'd found each other once more.
The place he'd been after the Veil had been good, peaceful... free. So while he'd known he missed the people he'd left behind, it was difficult to grasp just how much. Now, back in the world of the living, back within his own solid flesh and blood, Sirius realized that he'd missed Moony so much it physically hurt. "I'm sorry," he muttered to the top of Remus's head. "I won't. I promise. I won't."
It was an empty promise, maybe. Deep down inside him, Sirius knew either of them could disappear from this place just as suddenly as they'd come. But it was a promise he wished to Merlin he'd be able to keep. And maybe this time, that could be enough.