A Hard Question To Answer ?

Why are you trying to explain about more then what is needed for your question.... The things which you state in the detail of your question are things that if someone has an answer to it or even has an Idea of one already knows, kind of a waste of time to have a -ed lesson..... and you left out the part about females being programed to cheat too, since when they are ovulating they look for the strong well built mate (to reproduce with), yet during the end of the menstrual cycle we look for the healthy, caring, good father, teddy bear types (the one to raise the children). As for the question or how marriages or relationships are supposed to work (In my personal theory and experience)... We decide to make them work,(divorce is when you realize they changed from the one you love or realize you made a mistake ect) slightly against nature we pick someone that we care for enough to stop the urges or feelings for anyone else, If you are in love you don't see anyone else, its just them, Over all I guess we pick our hearts over our more primitive sides influences.