Hey, Christa -
I'm not a Romance writer, but I do write a romantic subplot from time to time. Here goes:
If he's really noble and honorable and interested in more than a short-term thing, he'll probably do everything he can not to let on that he's thinking about sex. He'll want her to be comfortable around him, and will probably go out of his way to make her so. He'll probably be a little confused, because the ways he's accustomed to dealing with people don't apply with her. And a little scared, because the love a soldier has for his buddies is nothing like what he feels for a woman he wants to court. It'll be an unfamiliar sensation.
As to what "ga-ga" feels like? His palms may sweat. His breath may get short. His chest may ache. It will be difficult to concentrate on potential hazards for wanting to look at her--another source of frustration for a soldier accustomed to watching for danger. He may be looking at her, realize she's asked him a question and have no idea what it was because he was too busy trying to memorize every line of her face. He may glance at her, ahem, assets and then curse himself (inwardly, of course) for not being a gentleman. You guessed it--confusion. Frustration. But he keeps at it because the frustration he feels around her beats the familiarity of the world he knows.
If she's in danger, he may start to panic--he's accustomed to dealing with hazards to himself, and the worst thing he can imagine is harm coming to her.
Of course, if he's not really all those things, he'll try to figure out the shortest distance to the inside of her skirt, stay there as long as he can, and not look back when it's time to leave. Then he'll try to contact her again a year later when he's next in town, and may not understand when she explains she's married now and can't see him.
Hope this helps. Sorry for horning in on y'all's forum.
HN