I'm sorry but I so completely disagree.
Regardless of whether or not jewelry or vows have been exchanged, once the terms boyfriend and girlfriend come into play that is a promise of monogamy unless both people have agreed to an open relationship.
Some people never intend on getting married. I was with hubby for 5 years before he proposed. I'm sure if either of us had strayed in that time we wouldn't be married now.
I state again, I hope you are cheated on one day by a girl friend. I hope when you go to propose to a girl she says "sorry, I've been sleeping around and you just aren't my first choice. Bye"
'People are never perfect but love can be. People waste time looking for the perfect lover rather than creating the perfect love' - Princess Leigh-Cheri from Still Life With Woodpecker.