That section of the library is not in the game yet (that's why it's grayed-out).
If you went to his bedroom after he showed you around the house and you already picked something intimate as well, just keep visiting and "have fun" with him, he'll eventually think he has enough influence and tries to push things further with you. The speed at which it happens is affected by whether you were submissive and went along with everything during the first visit or if you resisted.