fall off the wagon
to start drinking alcohol again after you have stopped

[TahlilGaran] Dictionary of Contemporary English ▲

fall off the wagon
to start drinking alcohol again, especially too much alcohol, after a period when you have not drunk any.
Six months later he fell off the wagon in spectacular fashion with a three-day drinking spree.

[TahlilGaran] English Idioms Dictionary ▲

fall off the wagon
to return to use alcohol or drugs after stopping for awhile
The man fell off the wagon after he had stopped drinking for three years.

[TahlilGaran] English Idioms Dictionary ▲

fall off the wagon
v. phr., slang, alcoholism and drug culture To return to the consumption of an addictive, such as alcohol or drugs, after a period of abstinence.
Poor Joe has fallen off the wagon again
■ he is completely incoherent today.

[TahlilGaran] English Idioms Dictionary ▲