Hi Mariel! You can think about this in two ways. From a literal perspective, it could refer to a situation in which people fall in love with a hero after he or she saves their life, but the hero does not reciprocate. However, you can also consider this phrase as an example of a literary device. Antithesis occurs when opposite ideas are introduced in close proximity with the same structure. "Saving lives and breaking hearts" fits this definition, with "saving" and "breaking" contrasting in meaning.
I hope this helps!
