The sound alone would have had an affect, but with her special superpowers attached, it was even more prominent. He returned the kiss and felt himself wanting more. A lot more if he was being honest, and he understood that he needed to stop this.
But maybe just a few seconds longer. Just long enough that he'd remember what she tasted like. Just long enough that he'd be able to call up that sound she made in his mind when she wasn't around. He pulled her closer, kiss getting harder as time moved on. He made a sound in the back of his throat, and that was what clued him in on the idea that he probably needed to stop sooner than later, or he was going to get himself into a lot of trouble.
It was with great reluctance that he pulled back, looking for all the world like it was the last thing he wanted to do.