Romance and love can outrank magic, technology, or even a PhysicalGod, in influence on the progression of a story. But how it influences the story is a crapshoot.
'''The Good:''' Love acts as a FixerSue or DeusExMachina, overcoming all.
'''The Bad:''' Love is an ArtifactOfDoom, corrupting even unambiguously good people who lack the willpower to sacrifice their relationships for their morals into a FaceHeelTurn. Murder mystery series seem to love this one.
'''The Ugly:''' Love is an ArtifactOfDeath, bringing doom and pain to all who encounter it.
'''The Complicated:''' Love is an embodiment of the RuleOfDrama, making life unnecessarily complicated.