He didn't exactly understand what that silence meant, apart from the opportunity to keep talking. Whether or not Regulus believed him didn't really occur to him-- because Regulus had to know. Somewhere in there, he had to know that James was telling him the truth. Because, why the hell lie about something like that?
"I told you you were going to get yourself killed," and a sort of tension between his shoulders snapped, something he hadn't been fully aware of until it was abating. He'd told Regulus a lot of things, actually, but he hardly felt the need to repeat them all. There was something a little apologetic in his tone, even if he didn't actually say he was sorry. And he wasn't exactly, even if he wished he hadn't. Because it was like he had been wrong, was it? Still. He wished he hadn't said it.
James sighed a little, his body relaxing. Relaxing was good. It was certainly better than getting wound up. Keeping his mouth away, more or less, from Regulus's, James rested his temple against the side of Regulus's head. The trade-off seemed decent enough. It skirted enough of what he ought not be doing without crossing the blurry line that kept forming and breaking apart in his mind.
"For the record: that had not been a suggestion." And it was a little less teasing than he'd perhaps been intending. Still, it wasn't quite critical, either. It just wasn't him to too genuinely decry trying to off Voldemort.