Some do it more than the others.. For instance, sleeping with somone else is definitely cheating for all but some might think that just a casual lingering of the gaze is not but then feeling attracted to anyone outside your committed relationship is definitely cheating according to me. That is precisely why my husband and I do not have any secrets, we save our passwords to our email accounts and we keep our laptops open without any passwords either.. So if I want I can just check his email and he can do the same.. Same goes for our facebook accounts, we have FB application on our iphones, ipads, blackberries and we can easily access each others profiles. So to avoid cheating, no secrets.