Good job finally taking steps to get yourself out of infidelity.
Sucks about the required year separation because your WW will not admit infidelity.
My advice.....
Stay in touch with POSOM’s BW.....
They are going to counseling and trying to see if they can work it out.....she will still be investigating, digging into details, and interrogating this shitbag OM.
(btw, imo there is a greater than 50% chance that this turd will NOT be getting a D and giving up half of his assets and time with kids if they have them.....so be prepared for your WW to try to come back to you once OM dumps her).
Let her know that you are divorcing, but would rather not wait a year because she will not admit the A.
Ask OBS to contact you if she finds any irrefutable evidence or if POSOM confesses.....
Let her know it will only be for leverage to get your stbxWW to admit the infidelity so you can get out of the mandatory year long separation before getting D.
And if OBS is able to get undeniable evidence or a confession, give it to your attorney and hit your WW with a demand for her to admit the infidelity and skip the year wait in return for you not exposing her behavior to friends and family.