To be treacherous or faithless to; betray; as, to go back on friends.(verb)
To fail to keep; to renege on; as, to go back on one's promises.(verb)
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Use "go back on" in a sentence
"Her heart was pounding as she rested against him, waiting, re-couping, confident in a moment — with warmth and gentleness and the promise of next week — he would say, "Let's go back on deck.""
"After the administrator and Marjorie Tench forced me to perjure myself in the press conference, they knew I couldn't go back on my word."
"Because the person knows too much about his organization: how much to offer a guy to go back on what's practically a done deal, which moneyman's on shaky enough ground to be bribed."