The phrase "on-again-off-again" refers to a relationship or activity that is characterized by sporadic starts and stops or inconsistency. Antonyms for this phrase include stable, consistent, reliable, dependable, steadfast, and continual. A stable relationship or activity is one that has a reliable and consistent nature, whereas a dependable one is characterized by faithfulness and trustworthiness. Steadfast refers to a quality that remains unwavering in its commitment, and continual suggests a persistent and unbroken quality. Therefore, if you seek to avoid the unpredictability associated with "on-again-off-again" relationships, seek stability and dependability in your current activity.