Sure, it´s possible to love more than one person at once, but in order for such polyamorous relationships to really work, meaning that all people in such a relationship are truly happy, there is an amount of maturity required which most people don´t even display in a "normal" relationship. For relationships to work, the people in it must come from a place of abundance and fulfillment, but usually people come from a place of lack and neediness, wanting the other person(s) to magically fulfill them and make them complete.