From Longman Dictionary of Contemporary Englishrun off with somebody/something phrasal verb informal1 SEX/HAVE SEX WITHto secretly go away with someone in order to marry them or live with them – used to show disapproval Liz shocked us all by running off with a married man.2 SCCSTEALto steal something and go away a conman who makes a habit of running off with people’s savings → run→ See Verb table
Examples from the Corpus
run off with • But the stepfather of the Idaho beauty objects to his daughter's running off with a commentator.• They nearly ran off with a second too.• There were some heart-stopping moments in the Town goalmouth, but they survived and nearly ran off with a win.• She ran off with breakfast for her respectable middle-class family.• After all this is the woman whose husband has just run off with Felicity Kendal.• I wanted to run off with her and raise our boys together.• Then he ran off with the wire, not out of the gate, but round to the front of the house. 