The phrase "on-again, off-again" refers to a situation that is characterized by frequent and unpredictable changes. There are several synonyms for this phrase that can be used to convey a similar meaning. For instance, "intermittent" describes something that occurs at irregular intervals or with breaks in between. "Sporadic" means something that happens occasionally or irregularly. "Inconsistent" suggests a lack of reliability or stability. "Unsteady" describes something that is frequently changing or unstable. Other synonyms include "fitful," "uneven," "irregular," "choppy," and "discontinuous." Each word captures a different nuance of the concept, but overall, they all imply a sense of unpredictability and inconsistency.