It's not his therapist he bangs, it's his teacher. They do have low-key date partway through the book, yes, which she quickly realizes was a mistake and a breach of ethics. She actually
rejects his later advances because of his advanced intelligence - she hates that she can't keep up and he's become an arrogant twat to boot, lording his newfound genius over everyone. She also acknowledges the deep gulf between his intellectual intelligence and emotional intelligence, and understands he's not, at that point, capable of making that kind of decision.
When they do finally sleep together, near the end of the book (which only happens ONCE, not the "lots of times" Larper would have us believe) he's severed his ties to the experiment, and his intelligence has declined to her level, and he isn't an insufferable twat about it anymore.
Not to mention, he's actually the one who breaks off the relationship, and she's devastated by it. She was literally the only person in the book who accepted him as a human, both as a retard and a genius. But sure, she totally just wanted him for his intelligence
