Everyone has their own preferences and certainly different cultures have their own unwritten and written rules about this behavior. When I went to the UAE as part of a defense conference for the U.S. Navy I was asked by several men if I was married and they seemed very consternated that my husband would allow/support me going away from him like I did. In their eyes, once you are connected to a person, even not married, there should be no one else in the picture.
When I was younger I had a boyfriend who insisted on a "no strings attached" relationship. I was head over heels with him and I allowed it. It was ok, but certainly now 2 years after my divorce I need the comfort of a person who will give me their undivided attention. I wanted to hand my boyfriend my whole heart and in return he gave his back to me.
Perhaps at different times in our lives we just need different things.