Since your marriage was sexless for a long time, there is a fair chance that she has met someone that she finds more compatible.
Whether she has or hasn't, she has obviously made up her mind that she wants a clean painless break from you. I will tell you this, most woman, not all, have someone else in mind when they leave. That is not always the case though, one of the posters here, Mojo, is divorcing her husband due to sexual issues and there is no third party involved.
No matter what you do, you are going to have a near to impossible time changing your wife's mind, in my opinion.
The reason I am telling you this is to setup a scenario for you. A potential to throw a cog in the works so to speak, but a risky one.
If you want to take the risk and skip out on the techniques you may have been using, let me know, I will give you some last ditch ideas, but please, only if you are serious.
It is also possible that the best course of action is just to let her go, clean up your issues, and then start over with someone more compatible.
All the best, -NOPkins-
I will ferret out an affair at any opportunity.
-An affair is the embodiment of entitlement, fueled by resentment and lack of respect. -An infidel will remain unreachable so long as their sense of entitlement exceeds their ability to reason.