Think it depends on the couple concerned. Tiredness, stress - and even disagreements all play a part in how receptive you are. Also, after a time, most relationships lose the inital impetus, and settle down into a less active pattern - but having an affair is never a good idea. Talk to your man, & see if you've outgrown each other or just fallen out of love. If true feelings were there in the first place, it should be quite easy to find out what's gone wrong, and to rekindle the flames of passion, but having an affair is never the answer.