Just caught up with your thread... if you rewind my sich about 12 months I put myself almost at the same place as you - except I didn't have this forum then. Caught W in an EA, she denied it but wouldn't break contact with OM. Wanted Open marriage and kept pushing it, even loured me into discussing spicing up our sex life with a 3rd... we went to MC, and she detached as I continued to push.
After I overdid it for her birthday she declared the ILYBINILWY and then moved out - that's when I came across this forum... about 6 months beyond where you are at. So consider yourself lucky that you found it so early and can detach early and not make the same pushy mistakes I did. Pressure only pushes them away!
If I were to do it all over again I would have found concrete proof earlier on of the PA (I backed off but never stopped watching her) and then given her an ultimatum or detached then instead of continuing pretending nothing was going on while trying to fix the R. That only pushed her more towards him.
A few things.. don't push MC it doesn't do any good if she doesn't want to be there. Detach now while you still can.
WRT the A... I know you probably don't want to hear this but sounds like a PA. I didn't think mine was but had suspicions and finally proved it out later on. (The OM and spice up sex were the clear cut indicators)
For finances, we came go an agreement which we both signed, no L's involved which I know some on this forum would advise against but it's been 4 months and she's kept her end of things.
Oddly enough despite moving out she's still very engaged around the house, trying to take care of things.
As to when to throw in the towel, I have been tempted many times over the last year but it passes, prayer and surrounding myself with pro-marriage friends help. I also look to my D and ask myself what kind of role model do I want to be for her.
Me: 40 W: 45 T: 13, M: 11 1 D: 9
Suspect A 6/15 ILBINILWY 8/15, and 3/16 EA/PA Discovered 3/16 EA admitted 3/16 W Moved out 4/16 W opens R talk and says A over 1/17