Well if you’re ready to D then you she let her know that you know what’s going on with the OM and that you will not live in an OM and that you will be filing for divorce.
Her response will tell you how to proceed. If she says ok then you file. If she says she wants to work on marriage you tell her you need to think about it.
I’m just warning you that once you go ahead with this you have to follow through. I also must warn you that if this has been going on for 2.5 years she is most likely going to agree to divorce.