The 3rd one

Love blossoms between two individuals, not more
Harmony can be achieved in pair exclusively, no sore
How can a third protagonist stick to a couple’s existence,
think there is a place vacant in their nest, is that romance?

Love reigns when two magnets are attracted to themselves,
when lovers grow stronger and stronger together like elves
A magnet being repelled should have the guts to find its pair
who is surely wandering all alone somewhere in deep despair