A brief excerpt from Leonard Peikoff's Objectivism:
The Philosophy of Ayn Rand
The fact that a man's sex life is shaped by his conclusions and
value-judgments is evident in every aspect. It is evident in the setting he
prefers, the state of dress, the caresses, positions, and practices, and the
kind of partner. This last is particularly eloquent.
No man desires everyone on earth. Each has some requirements in this regard,
however contradictory or unidentified and the rational man's requirements, here
as elsewhere, are the opposite of contradictory. He desires only a woman he can
admire, a woman who (to his knowledge) shares his moral standards, his
self-esteem, and his view of life. Only with such a partner can he experience
the reality of the values he is seeking to celebrate, including his own value.
The same kind of sexual selectivity is exercised by a rational woman. This is
why Roark is attracted only to a heroine like Dominique, and why Dagny Taggart
in Atlas Shrugged is desperate to sleep with John Galt, not with Wesley Mouch. Romantic love is the strongest positive emotion possible between two
individuals. Its experience, therefore, so far from being an animal reaction, is
a self-revelation: the values giving rise to this kind of response must be one's
most intensely held and personal.
When a man and woman do fall in love assuming that each is romantically free
and the context otherwise appropriate sex is a necessary and proper expression
of their feeling for each other. "Platonic love" under such
circumstances would be a vice, a breach of integrity. Sex is to love what
action is to thought, possession to evaluation, body to soul. "We live in
our minds," Roark observes, "and existence is the attempt to bring
that life into physical reality, to state it in gesture and form." Sex is
the preeminent form of bringing love into physical reality.
The subject of sex is complex and belongs largely to the science of psychology.
I asked Ayn Rand once what philosophy specifically has to say on the subject.