Great advice here. If you are at the end of your rope and she refuses to quit contact with OM, you can and probably should give her the ultimatum to leave, and possibly file for D (you can always cancel that).
That said, I'll tell you how that went with me. Every situation is different, so take this for what its worth (I am divorced and remarried now).
W was in at least an EA for about six months and then I proved it was going on after lots of denials.
I was wanting her to stop the A so we could work on M. I told her to just pause the A for six months and see where things go with us. She wanted no part of it. Said M was over.
So, I told her she needed to leave or stop communicating with OM.
She refused and instead started sleeping in another bedroom.
She finally moved out about a year later - it was the hardest period of all before she actually moved out - having to live in the same house under those conditions was tough but I refused to leave. If she wanted to have a R outside of her M then she needed to go.
Once she moved out I felt a ton of relief. I shortly after filed for D when I met someone else.
Subsequently she figured out that the grass isn't so green and wanted to come back but I had moved on. She still to this day regrets the whole thing I have heard.
So, in my case it took her actually leaving and me moving on with someone else to get her to wake up. By that time I wasn't looking for her to wake up, however. I was done. You may be as well at this point given that she is not turning back, so it might be time to start the process of getting her physically out of the house and possibly filing for D. She may wake up, but do all this based upon what you are ready for, not what she might do.
ME/XW:47 S21, D19, S15, S14 M:21 T:26 W moved 6/10 I filed 7/10 D final 4/12 remarried 8/12 W wants to R 12/10 and 4/11 but I decline