Lost love functions like a forced character evolution, stripping away a protagonist's comfort zone. I've seen it used as a catalyst for brutal self-reliance, especially in fantasy or post-apocalyptic settings. The character who defined themselves by that relationship has to rebuild from zero, often discovering a colder, more pragmatic version of themselves. In something like 'The Poppy War', Rin's shattered connections directly fuel her descent into vengeance and power, redefining her moral framework entirely.
Sometimes, though, it pushes growth towards healing, not hardening. In quieter contemporary fiction, the loss creates a vacuum that forces introspection. The character might finally learn to sit with loneliness instead of fleeing it, or rebuild their identity on their own terms. The growth isn't about becoming stronger in a combat sense, but about developing emotional resilience and a more integrated sense of self, separate from any partner.