My WW says I am fixating on this too much and should focus on fixing things with us more.
One element that commonly accompanies cheating is gaslighting by the WW. Per your description, your WW has cheated on you more than once, over a period of years, and has among other things enjoyed the active encouragement of her friend, whom you also know.
To accomplish all of this, your WW must have formulated and communicated thousands of lies. A web of lies. I reckon that, like most cheaters, her weaving of this web was insidious and cumulative. I point that out because she has been lying to you for a long time, in a profound and paradigm-shattering manner. Lying is her normal. You should keep that in mind as you filter the words she utters to you now.
The fundamental goal of gaslighting is to manipulate the victim into doubting not just factual truth, but even his own moral and emotional truth. This position by your WW vis-a-vis a woman who has behaved as nothing other than an enemy to your marriage is classic gaslighting. The answer from you is not just "no" but "hell no!!!"
At the very least, you should personally stay away from the wedding. I would suggest you also let your WW know that her choice to elevate the friendship with an enemy of the marriage, over the completely legitimate and normal emotional need of her BH, will tell you what you need to know about her commitment to the marriage.
Gently, I'd suggest also that you go to the Healing Library on this site and do some reading. Also, read some of the threads on "Just Found Out".
Among other things, you should read about The 180. This is a technique to give yourself some psychological space so that you can start seeking your heart's truth. I'd suggest also seeking a good IC, one with experience dealing with the sexual and emotional trauma of having been betrayed.
On the subject of counseling, the general advice here is to eschew MC this early after Dday. Most MC's lack the skill to deal with the trauma, emasculation, sexual humiliation a man experiences when his wife cheats. Has your MC encouraged you to examine your role in the cheating yet? Has the MC allowed your WW to get away with using the "M-word" euphemism ("mistake") in referring to her thousands of conscious decisions that she would rather treat her half of the marriage as a secret, one-sided open marriage than honor the promises she made directly to your face when you were wed?
That advice is especially apt in the case of a long-term recidivist cheater like your WW. There is something deeply broken in her moral compass. She is not trustworthy nor honorable. Until she figures out what is broken, fixes it, and makes herself into a trustworthy person, then you are attending MC and trying to patch up a marriage to a pathological liar and recidivist cheat.
She has ended all affairs and says she wants us to be together, says she loves me, that she never loved these guys, etc.
How can you know she has ended all affairs? How can you even know whether you know about all affairs?
"Says she loves me, that she never loved these guys, etc." Said every cheating wife caught by her BH, ever.
[This message edited by Butforthegrace at 9:39 PM, Friday, March 3rd]