My sentence for the first half: The conflicting desires to either celebrate or annihilate beauty are the two sides of the same motivational force that I understand as central to our existence.
My sentence for the second half: There is also a painful contradiction in the way we sometimes betray love in order to hurt it, only to then rush in too late to protect it with our own efforts.
My response: When Montague refers to the "double edge of impulse," he means that our instincts and desires can lead us to both create beauty and destroy it, illustrating the complex and often conflicting nature of human emotions and actions.