Sentence:  'Would you ever <WSD>play up</WSD> on me given the chance?' asked Stacy./ 'Never, why?' asked William./ ... 'Oh! Just when I was younger, I had a few guys take me out and when I didn't put out in the first week, it was the last I would see of them,' explained Stacy. 
Meaning of the word marked with <WSD> tags:  To be unfaithful to a lover; to cheat; used with "on".