the only real difference between before and know (to her) is that YOU KNOW about the affair.
she is going to try to dither in the middle as long as possible, "not choosing" between you and him.
of course "not choosing" IS A CHOICE - its choosing him.
the hardest part is going to be getting her to realize this. you arent going to get her to this realization by being "nice". you will get her there by pushing her off the fence.
in sales its called the "take away". make her feel that her choice HAS cost her you, her lifestyle, her family, and everything else that she has been taking for granted.
affairs thrive on secrets and the thrill of the forbidden. they tend to quickly die under the glare of the light.
if the OM is married or has a girlfriend, tell them.
tell your family, tell her family that she is having an affair. ask for their assistance.
tell mutual friends and ask for their assistance.
normally, in the case of a remorseful wandering spouse id say think carefully about this step (telling people) but ... in the case of a spouse still in the fog ... do what it takes.
keep telling her you are sorry that she has made the choice to be with the other man and that her choice of "her secrets, her affairs, her lies, and her cheating" over you, your family, your child, your marriage, and your relationship has consequences. one of those consequences is losing her family, the marriage, the relationship, and the lifestyle she has become accustomed to.
ask her when she plans on moving out and if she wants help packing her trash. offer to pack it for her.
ask her when she wants to make an appointment to go see a lawyer together to discuss divorce.
each of these questions drives home how her choices have consequences. keep repeating that you it pains you that she choose "her secrets, her affairs, her lies, and her cheating" over you, your family, your child, your marriage, and your relationship".
dont ever paint yourself into a corner. leave room. a trip to the lawyers doesnt mean you sign right then and there to divorce. asking when she plans to move out doesnt force her to move out tonight. dont make timelines ... not yet. just keep pushing the unpleasant consequences in front of her.
be aware the other man "might" come by the house while you are out...
after all, they are in "love" and acceptable behavior or even intelligent behavior isnt to be expected from them.