Remus wasn't so much surprised at the outburst as he was touched. Still, the guilt didn't leave him. He knew the truth, even if he didn't push it; if he hadn't hurt Sirius, if he hadn't pushed him away, Sirius would've been there.
"I have no right to expect anything after the way I behaved. The way I treated you. I'm sorry." Then Remus shook his head. "You couldn't have done anything, anyway. The moon was still fresh when I... well, when I landed. You couldn't have prevented it. You might have found me earlier than James did, but... It doesn't make any difference now. It wouldn't have made a difference."