This reflects an opinion and a motto that I chose to live by. Sex is just an activity, such as going to the gym. It is great stress relief, awesome for cardio and pleasurable. Because of so many failed relationships, sex as just an exersise, keeps the emotional link people make to it out of the picture.
When emotions get all involved, a lot of times other stressors come into play because of possession issues, jealousy and the human want for love and affection.