Regulus swore his heart was beating nearly as fast as Peter's resting pulse. He stood slowly, trying to gauge if everything was safe. Lupin never seemed prone to fits of impulsiveness. Everything he'd observed told him the young man was steady, reasonable and perhaps even kind. Patient at the very least if he put up with his brother and Potter both.
The minute he'd been made aware that Lupin was there, he'd found himself somewhere else to live. It'd been plain for a very long time that Sirius hadn't wanted him around and he didn't want to intrude on whatever their usual was. He didn't need to be the nargle in the corner.
"Likewise," he said with a little nod. "I was just heading back." An acknowledgement that Lupin also probably came out there for solitude. He took a step back and turned away, pausing to say. "Please don't tell anyone."