I think sexual behaviour is just that: behavior. We make decisions about who or what we act with, and whether to begin - and it is often only whether to begin over which we can exercise willpower. Illicit behaviour feels exciting because the anxiety that accompanies it causes adrenaline that in turn boosts pleasure, just like a turbo system boosts the energy in a car. Then ordinary activity is still pleasurable, but it lacks that extra 'something'. Which is sad, because we lose our sensitivity to enjoy life the way it was made to be enjoyed. Sensitivity can be regained of course, but only by abstaining from the illicit behaviour and retraining ourselves, when we are ready, to enjoy things in a proper way.
Ephesians 4:19 (NIV) "Having lost all sensitivity, they have given themselves over to sensuality so as to indulge in every kind of impurity, with a continual lust for more."
