Tonari no hito (2004)

Lonely Masako, trapped in a loveless, childless marriage, finds the monotony of her days broken by a series of anonymous love letters inviting her to a secret liaison. A chance meeting with her neighbor, Suzuko, convinces her to make one last desperate attempt to re-ignite the passion in her marriage. However, the consequences of that action propel her in a new direction to look for fulfillment, leading to an unexpected destination.