Hermione turned away so that he wouldn't see her blush. So... he could smell her arousal then. Interesting. It's not like she had any control over it. She was finally back in the presence of quite literally her first and last love. They found comfort in each other during the war on lonely nights in the tent. They'd  planned  to continue their relationship on a more official basis when the war ended, but they'd never gotten the chance. Now, she had him back along with the opportunity to never be without him again. It was a heady feeling. 