I think Maytag's analysis is right on the money. Crest is usually nervous around pretty women because... well that's NORMAL, especially for a virgin and especially for a guy who's been BURNED before. Any guy who ISN'T nervous around pretty women, is some guy women shouldn't be going near, at least not willingly. Those guys tend to treat women very badly. With Suspira, she's also a level 3 "genius" mage. The sleep depriving fear is well justified. Now as for asking him to her bed, well. We don't know HOW LONG Suspira and Kin were an item. She could simply be accustomed to needing a warm body, and to Crest's credit, he has shown he knows how to keep her safe.
So Crest, keep being nice to her, treat her well, and we'll see how this goes.