For this, let us examine what is involved in romantic love. It is obvious that romantic love happens between opposite sexes. The man is enchanted with the feminine persona, her manners, her softness, her demurity, her vulnerability..
And then there develops this need to possess. What is the relationship between exclusive possession and romance?
Is romance primarily a need of the ego? Romance is always characterized by expression of mutual praise and affection, which usually includes physical closeness as proof. That would explain the need for exclusion, for the very nature of ego is separation.
Is romance primarily an expression of the sexual urge? The sexual urge is important because it is the most concentrated form of pleasure. In this case too, the consciousness of the other, physically or psychologically, is detrimental to full enjoyment of the act. Sex is usually done behind closed doors, at night, in privacy, and quietly. An extremely important factor in this is the social taboo about sex. Sex is considered unspeakable, unwatchable. Why?
The human animal is made aware by various kinds of influences, religious and otherwise, that sex is a capitulation to sensation, and unworthy of a man or woman of greatness. It is considered a "base" instinct which leads to bondage and to being a "householder" who can only be a mediocre person. Marriage is an admission of this need, and perhaps the vast amount of celebration associated with marriage is an attempt to cloud, in the ensuing noise, the shame associated with it.
Sex is also intimately linked with love, and as love is dependant upon the continuation of the illusion of being a separate self, every lover knows, at some level, that his/her love is basically selfish and a device to psychically gratify himself/herself in the most devious way possible.
Hence, there is this sense of guilt in sex. Any sign that one is actually a sexual animal is hidden and the /motivations/ of cosmetics and of looking "sexier" ignored. They are considered part of "beauty", the sign of desirability.
During the sexual act, the height of pleasure can only be obtained if one is fully immersed in it, without a thought of anything else. And strangely, one demands complete immersion from the other as well. If even a hint of the fact that the other person is not really interested is there, it dilutes the pleasure of the act (for the psyche).
Sex is also self-forgetfulness. Since most of us feel inadequate at various levels of our existence, sex remains the only act which makes us feel adequate and complete.
And since observation by another would thus make one conscious of oneself and of one's inadequacies, privacy is desired.
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