For what it was worth, Illya wasn't analyzing anything at this point. As soon as she took his tie off, that was the final signal that he needed to ensure that Gaby wanted to do this as much as he did. Perhaps he was acting on instinct or reaction to hormones. All he knew was that he wanted.
Making their way into his bedroom, he placed her down on the bed, then got down on his knees in front of her. Even on his knees he was practically taller than her. From this angle though, he could easily reach behind her and unzip her dress. Once the zipper was down, his hands moved up her back from the small of it to her shoulders, brushing over her warm skin and catching on where her bra was clasped. Illya would come back to that in due time.
"Ya tebya khochu," he murmured, as if she wasn't aware of that already.