I'm not one for sex scenes, but I understand it's vital for the story. It shows how evolved Helper has become and confirms a lot about the protagonist's affiliation to robots and detachment to humans. It is, however, very curious that Helper designed her body to facilitate intercourse. She's turning out to be quite manipulative, like any human. I have one thought: his mask was off! She saw his face!

She brushed a few strands of hair from my eyes, and wiped away my tears.

I assume he put it back on before Madeline saw it? This is a big deal.