Well, most of us were never trying to be poly--we just found it perfectly natural to be attracted to and involved with more than one person at a time.
When the song asked "did you ever have to make up your mind?" my response was to wonder why I had to choose only one. Why couldn't I be involved with both girls?
(I realize that song may be too old for some folks to catch the reference. That's OK...I've adjusted to being old.)