How we cite our quotes: (Part.Chapter.Paragraph) or (Part.Paragraph)
Quote #1
Cecilia felt a pleasant sinking sensation in her stomach as she contemplated how deliciously self-destructive it would be, almost erotic, to be married to a man so nearly handsome, so hugely rich, so unfathomably stupid. He would fill her with his big-faced children, all of them loud, boneheaded boys with a passion for guns and football and aeroplanes. (1.4.36)
We never actually hear Cecilia express sexual desire for Robbie—the library scene is all from his perspective, not hers. That means the only person we hear her kind-of sort-of lust after is Paul, who she thinks is so awful that it would be "almost erotic" to marry him. Maybe this "deliciously self-destructive" impulse is what draws Lola to Paul as well?
Quote #2
"Bite it," he said softly. "You've got to bite it."
It cracked loudly as it yielded to her unblemished incisors, and there was revealed the white edge of the sugar shell, and the dark chocolate beneath it. It was then they heard a woman calling up the stairs from the floor below [...]
Lola was laughing through her mouthful of Amo. "There's Betty looking for you. Bathtime! Run along now. Run along." (1.5.74-76)
Paul urges Lola to eat his chocolate bar. It's not stated explicitly, but this is probably the moment before Paul's first attack on Lola. Remember from the discussion of chocolate in the "Symbols" section that Amo is linked to both violence and sex or love. Paul urging Lola to eat the chocolate is the closest we get to seeing the rape. It's one of the queasiest scenes in the book (and also one of the queasiest scenes in the 2007 film).
Quote #3
A drop of water on her upper arm. Wet. An embroidered flower, a simple daisy, sewn between the cups of her bra. Her breasts wide apart and small. On her back a mole half covered by a strap. When she climbed out of the pond, a glimpse of the triangular darkness her knickers were supposed to conceal. Wet. He saw it, he made himself see it again. The way her pelvic bones stretched the material clear of her skin, the deep curve of her waist, her startling whiteness. (1.8.2)
This is Robbie remembering Cecilia coming out of the fountain in her underwear. It's important that we see his perspective in retrospect; that is, we don't hear his thoughts at the time, but only later. Cecilia becomes an image, or a character, in his mind. Sex is about stories as much as acts (which is why the act is set in the library, perhaps).