soda machine break up
A relationship that takes several break-ups and make-ups to end, rather like trying to tip over a soda machine by rocking it back and forth.
"Did Jack and Jill get back together again? This is like the fourth time"
"It's a soda machine break up. Give it time, they've almost got it tipped over"
"It's a soda machine break up. Give it time, they've almost got it tipped over"