My first husband cheated on me, throughout our 20 year relationship. I had no idea, until about 16 years in, and then I took a few years to leave him.
Some gems from him, on learning that I was leaving :
-
I'm going to convert my parents loft into a bedroom, and the children can live there without you (50 miles away) 
-
You will live to regret this (erm, no, I won't)
And my personal favourite, after weeks and weeks of begging me not to leave....
"Oh just fuck off then, sex with you was like fucking a corpse anyway"
Gaaah