I believe that its possible, but it's not for me, at least not in a romantic sense.
In general however, I think its absolutely possible to love more than one person. However, I do believe that there will always be different levels of love, and romantically, I think you will always love one person more than another.
I think there is something you take away from a relationship when you love more than one person romantically. You can never really give yourself to that person 100%, or have them do the same for you if they are also having a romantic relationship with other people.