If anyone had asked Nik, he would have said that he didn't consider his words a rejection, at least not in the long run. Immediately, yes. But beyond tonight? Definitely not. Apparently Sasha didn't - or couldn't - grasp that, and her huffy response saddened him.
He felt bad that he'd hurt her feelings in the now, even if he thought she might appreciate it later. Well. He hoped she would, otherwise his saying no was completely pointless.
"I'm just trying to look out for you," he said gently, "I don't want you to be angry later or have regret."