She has proven to me her trust with my brother.
If your wife is still in ANY CONTACT with your brother she is not being trustworthy. Nor has your wife proven she is trustworthy in any way. She has proven that she is profoundly untrustworthy. Saying that she can be trusted around your brother is about like saying she is a good drunk driver. No one should be trusted to go drunk driving. That is risky, irresponsible behavior. If your wife sees your brother, then she is being irresponsible and is playing Russian Roulette with your marriage.
This is what I mean by very poor boundaries. Your wife has none, which is exactly WHY you find yourself repeating this over and over again. There was no recovery from that affair, or this would not have happened again.........and again.
And I ask again. Is your brother married? If he is, then his wife should be told the truth. She should know that your wife is dangerous to her marriage even if they weren't married at that time. Hiding this affair from your family is a crime, CB, that only serves to harm your wife and leave your family vulnerable. I would suggest that sweeping this affair under the rug has not helped anyone, most of all your wife.
You said your wife has "recovered" from her affairs, but I see no evidence of that whatsoever. Did she even apologize to all the victims? Did her affair partners have wives and have they been informed? Because that is an essential part of recovery. Did that ever happen?
Christian forgiveness should always be based on REPENTANCE. Your wife has never repented. Repentance means to TURN AWAY. When has she ever turned away from her life of cheating? She has had 4+ affairs, CM. She is a serial cheater. That ain't repentance, my friend. Repentance means you turn away from the behavior altogether, not that you just rob a different bank. She has just robbed a different bank.
I suspect that you have been so eager to just "forgive" in the past that it has had the practical effect of
LOWERING THE BAR. She never had to do anything to change her behavior which should have been an expectation of rational forgiveness. Forgiveness should be more than a feel good measure to show how holy moly we are, it should also include a strategy to make sure it doesn't happen again. A true repentance.
And lastly, your problem here is an AFFAIR. Your wife had an affair. This thread belongs over on the Surviving an Affair where folks know how to save a marriage from an affair. I would click on mod notify and ask the mods to move this to the Surviving an Affair forum. Yes, your marriage has problems, but her affairs are the sinking Titanic and there won't be a marriage to save if you don't stop the sinking. That is why I say that focusing on porn use is a needless distraction. Stop the sinking first, my friend. Most people don't recover from 2 affairs, much less FOUR, so I would implore you to fix the most pressing problem by affair proofing your marriage FIRST.