Alec was extremely giving during sex. Because it wasn't an obligation. He wasn't owed anything. The other person wasn't owed anything. It was a coming together of something that was meant to be leisure, that was meant to be fun and feel good. If you weren't generous during that - then there wasn't even a point to it. Lenore could have literally given him any order and he would've done it, because sure, why not? This was for her too.
But she told him to undress her. Not strip her, not take off her clothes, or get her naked. Undress. It was oddly adorable, and the adorableness did not turn him off at all. Virtually nothing was a turn off to him. But also - she wanted him to get her naked, and he was a hundred percent on board with that. He sat up with her pull, and reached for her.
He stroked his hands up her side, pushing up her shirt in the process, but it wasn't fast or impatient. His fingers skimmed over the contours of her ribs before he pulled off her shirt over her head. He visually drank in the sight of her like that.