"Not like that," Regulus protested. "We got on well right from the start, that's all. Even then, before Bellatrix, I liked him enough to feel guilty about what I was doing to him because he was such a nice, friendly fellow." He shrugged and smiled wryly. "Simple friendship with no strings attached or self-serving angles was something of a novelty to me back then."
He didn't want to think he might have been harboring an attraction to Gaius all this time, because that would put him firmly back in the position of nursing an unrequited affection for an unattainable Snape again, not to mention dredge up all the old rivalry issues regarding Sirius. He had been exceedingly careful about both Gaius and Harry because of Sirius, trying not to get too close, trying not to do or say anything improper, all in an attempt to prove he was not the troublemaker he had once been.