Monogamy

     Not saying that I have anything against monogamy, but I was thinking... Where did the concept from from?  Who decided that people in a relationship must commit to only their relationship partner?  I see how it could just make sense - animals like lobsters and doves mate for life, people in love might only feel attracted to that one person, it would protect your partner from disease, and if it takes two people to procreate, it seems logical that a relationship should only include two people.  But, as I see it, a person may love someone, and be in a relationship with them, but just because they love one person doesn't necessarily mean they don't like other people.  So why can't they see people outside their relationship, while only feeling an intimate connection to their partner?  I just don't understand where the basic monogamy principle came from.  Who decided this?  And why?