see under off and on.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
How to use on again in a sentence
Over time, their potent mentor-mentee relationship evolved into a passionate on-again, off-again love affair.
No word yet if her on-again-off-again boyfriend, Justin Bieber (who is also an NEO ambassador) will be at the show as well.Anna Wintour’s Boyfriend in Hot Water with IRS, Juicy Couture Founders Ink Book Deal | The Fashion Beast Team | January 29, 2013 | THE DAILY BEAST
They may, however, involve those with whom you are on-again-off-again.
The 24-year-old Buffalo native had a "date" that night, but she wouldn't tell her on-again, off-again boyfriend with whom.
Morton depicts Angelina's relationship with her brother, James, at the time an aspiring director, as close but on-again-off-again.