Honey "gently"...this is going to take a really long time for you.
You gave her free reign for far too long. You let her walk all over you like a doormat. I am so angry for you.
Nothing is going to get solved till she goes and puts in some serious time with an IC. I read in "Not Just Friends" that when married women have affairs they are basically emotionally out the door and given up on their marriage.
Yours does not seem that way. She has personal issues. Is extremely sexual (appetite) wise...I wouldn't be surprised if she has voyeurism addictions. She doesn't sound like she wants to leave you...but she definitely wants her cake.
I think she keeps all the pics...because she enjoys the high intensity of the sexual encounters. Something kinky and unusual. He probably feeds her all type of shit to feed her ego using sex. She is just his toy.
I don't think it is ever too late for a revenge affair. Your affair altered her self-image...scarred her. She probably didn't do it for revenge, but to compensate for the hole your affair caused. If she has always had self-esteem issues...your affair intensified it.
You need to go NC...that means no more outings...or Birthday parties. Complete transparency with phone records as well. You may not have proof of what is being said, but you will have proof if the number is called. Of course it would be a lot easier if you block the numbers too.