A very interesting question indeed!
I will answer your question with proper evidences and not by my personal comments. This phenomenon of 'in love with more than one person (be it man or woman)' has attracted the attention of many psychologists. American psychological investigations presented a complete report of a survey conducted on 100 individuals. In this, 25% men acknowledged that they loved more than one woman. At the same time, they also confronted that the relationship level is complicated. Though they enjoyed the experience initially, but actually felt relieved when it ended. It was also obvious from their responses, that when they were emotionally involved with two women in their lives, they preferred one over the other for some particular reasons.
The reasons when identified made clear why man preferred to chose more than one woman in their lives. Often man does not get what they dream about from their closest love, hence they start finding other women who will return them with the much anticipated, dreamed about expectations.
Hence the in-depth reviews made very clear that there are two types of love existing in a relationship. 'The passionate love' or 'The Comfortable Love'. Significantly, none of the individuals chose passionate love. They acknowledged that they would never go for a passionate love relationship in both cases or comfortable love relationship in both cases. However, it is still alright to have a combination of one partner being a passionate lover and another being a comfortable love with more preference being given to the comfortable lover.
When individually, they were asked about the idea of being in relationships with more than two women, they gave a surprised expression with a feeling of negative exasperation (Wilraker, 2005; Jankowiak, 2006). They confirmed that being in love simultaneously for a long period would be a pleasant or satisfying experience for them as it would bring complications, unnecessary expectations. A 36-year old man as a subject confronted that love is a strong, powerful bond which can be maintained by only one person for a long time. The other transient relations are mainly because of our unfulfilled desires which, when get satisfied, people look for comfortability.
To sum up, the consequences of this investigation show that though human beings are sexually polygamous but fervently they are monogamous!!