I suspect that most people, in their heart of hearts, are "polyamoralists." That is, they are capable of loving more than one person at a time.
If your curious, here are some sites that explain "polyamory" in detail:
- The Polyamory Society
- Wikipedia - Polyamory
- Alternatives to Marriage - Polyamory
- Daily Mail News Story Featuring a Polyamoralist
In fact, if the figures on sexual and emotional infidelity are correct, then it seems that many people unknowingly participate in a critical aspect of polyamory. A "pseudo" polyamory, in the sense, that they experience love for more than one person, but they attempt to hide it. A true polyamoralist is honest and open about his/her feelings and desires.
Why do so many people only practice the more scandalous part of polyamory; that is, the sexual and emotional aspect of loving more than one person?
Because love and sex are full of double standards due to competing interests. What's good for me when it comes to dating, is not necessarily good for me to date. So, while everyone may have some polyamoralist tendencies, few people want to be involved with someone like that.