Well, Daval himself threw a wrench into that theory of yours with the most recent update of Immoral Desires:
Daniel states, "I guess I will have to masturbate to dreams of mom,
just like old times." Daval may be contradicting himself with having Daniel state that, because like you, I thought Daniel's attraction to Lana "awakened" when he saw her in her night wear. But even that itself was a rather nebulous premise because it's hard to imagine, Daniel, presumably 18-19 years old, has never seen what his mother looked like in her night wear once before the start of Chapter One. This line on page 11 (Chapter 12) would suggest that Daniel has been attracted to Lana since before Chapter One because not only would he daydream about his mom, but also he would masturbate to the thought of her.