If there is no monogamy agreement - implied or implicit, then dating other people should be expected. If both or either believes that they are in a monogamous relationship - and the one that is dipping isn't honest about where s/he is in the relationship, then that deception is wrong.
Yup. I think it is SO important to have a mutual understanding and it often gets overlooked when caught up in the feelings of being "in love" I'm from the class where your boyfriend girlfriend first, then engaged and then married and then a lot of us rely on that ladder as well..its realistic so you really have to be strong if you find yourself watching things go another way....I don't know any other patterns of dating that's been promoted...along with making a commitment in the beginning, both are very successful. I truly believe that it is up to the two people to make a serious effort to be a happy couple, agree to live like that, be like that....