fucking around

Cheating on someone, usually said in bitterness or anger.
Not just kissing, but more. See def 1 for 'fooling around'.
Oftentimes 'fucking around with' or fucking around on'.

for example:
"How dare you accuse me of fucking around on you!!"
or
"I knew she was fucking around on me with John."

by ajavudit September 01, 2009