My brothers wife cheated on him with one of her colleagues. Eventually he left her, when it was just too obvious that she was definitely cheating.
He had indisputable evidence including:
-he found an email from her lover to her saying alot of stuff including he didnt regret when they made love
-she called him by mistake from her phone in her pocket and she was with this guy and my brother heard her saying 'oh baby remember thats the bar we hung out in when we wanted to go make out where nobody knew us'
- one day my brother came home a day early from a trip unexpectedly because he was supicious, and the safety chain was on the door  - and this guy was in thier house!! she said a bunch of them had gone out and he was just drunk and she said he could stay the night and she put the chain on the door so he wouldnt leave and drive home !! he left an hour later though when my brother turned up!

And all other kinds of suspicious behaviour like staying out for days.  I always suspected she had borderline personality disorder but hes my brother and i knew he had to make his own decisions..
But I was happy when he finally admitted to himself what she was and he left her.
That was a year ago and she has pursued him relentlessly begging for another chance and that all she did was kiss this other guy on the cheek. she swore this up and down. but he didnt believe her and filed for divorce.  Their divorce was about to become final when she turned up with copies of 3 differnet polygraphs, notarized by the state (?) saying she didnt cheat and she passed.
So despite all the evidence he had, he has chosen to believe her now and has gone back to her.  Oh dear
Lots of people forgive thier spouses for cheating and go back and give it a chance and thats fine.  But I know she is still lying and hate the thought that he has gone back to her on the basis 'that she wasnt lying after all'.  I just dont want him to be hurt again.
So what gives?
If anyone give me a professional opinion on this matter, I would appreciate it.

My wife recently passed a polygraph for infidelity. The 35 year police veteran examiner said she was 100% innocent. There was no video. No chart I could look at. No summary of the questions. He said she loves you a lot and has done nothing wrong. I have a hidden audio of her indiscretions. I had played this to her before {the polygraph} but it had a lot of noise although you could still make out what was taking place. I have recently through forensic audio software cleaned the audio up. I played it to her and she broke down and confessed. So a cheating person can pass a polygraph.