I have to agree with Puppy. It almost killed me (literally, lol!) but to this day I have NEVER told my H how I found out all I did. Now keep in mind this started in March of 2008. As of Nov. 2009 we were LEGALLY separated.
My H started his affair sometime in early 2008.
I told him flat out I knew (after 8 months of collecting VERY solid info) but did not tell him I knew until our legal case began.
To this day it eats at him that he has no clue who told him (and if he knew how many people told me, including the higher ups at his company he would die).
He was plain awful to me both emotionally and legally so every so often I would say something very specific that would stop him dead in his tracks.
The day our divorce is final ( and not one minute before) I plan to hand him a big envelope with EVERYTHING. He lives with OW now and he will learn the hard way that his "roommate", co-workers, boss, company higher ups and "friends" aren't quite as loyal as he thought. This envelope also has signed affidavits (saved them in case my attny and I needed them in the future, lol!), photos, phone records... you name it. And it is safely locked in my attnys office.
Every so often he will try and get under my skin by accusing me of having a "mole". Ha! I never knew a thing about it until people started contacting me.
It is SO HARD but trust me, don't reveal your sources.