That Sirius was able to touch him and not recoil, especially considering how the war had widened the gap between them the first time around, helped ground Regulus. It helped, too, to know he wasn't alone in this; he wouldn't have to face the Dark Lord alone, and he wouldn't be turned over to Him. Or worse, to Bellatrix.
"Right." He drew in a deep, calming breath and released it slowly. "Let's find Harry. Then I'll do whatever you want me to do."