bit on the side
Noun
Meaning
bit on the side (plural bits on the side)
(slang, Britain, New Zealand, Australia) A secondary lover, a mistress.
I'm married to Paula, but Jackie, my bit on the side, is far more fun.
Synonyms
adultery
infidelity
leman
cuckoldry
kept woman
unchastity
two-timing
side chick
side piece
side bitch
side ting