A phrase used to indicate that a romantic
or sexual relationship
has ended, or is, as when the wheels do fall off a wagon, kaput. Sometimes heard as "wheels fall off the wagon" or "wheels falling off the wagon"
"She found out he was also shagging her brother
and so the wheels fell off the wagon then."
"Her incessant screwing
around on him made the wheels fall of the wagon, and he dumped her."
"If he keeps that up, I can see the wheels falling of the wagon soon."