What is the term for the ending of a relationship initiated by one partner?

The term that best describes the ending of a relationship initiated by one partner is "relationship dissolution." This concept specifically refers to the formal process of ending a romantic relationship, often involving the legal or social acknowledgment of the relationship's termination. It emphasizes that one party has made the decision to end the relationship, leading to its dissolution.

In contrast, "relationship termination" is broader and can refer to any cessation of a relationship, while "relationship breakdown" typically denotes a deterioration in the relationship rather than a formal ending initiated by one partner. "Relationship reconciliation" involves the process of restoring a broken relationship rather than ending it, which is not applicable in this context.