I have delayed adding to this as I am about to go through this myself. My wife went into full cult mode a few months back. We got past the initial discussions and it hasn't come up since. However, I'm about to tell her I'm done with being a witness. I've been working on getting up the nerve to tell her. I've even written her a letter, put it in an envelope and put it away for now. I'm not trying to be mean to her. It's not about her.
Ever since our discussion a few months back, she has been gobbling up everything JW. Studying more, watching JW TV a lot, etc.
I think my situation will turn out a lot like yours. The thing is, I don't want to be with someone who I can't be open with. The irony of that is that while I know this will probably end the marriage, I don't want to hurt her in the process. Sadly, though, there really isn't a way around it unless I just keep everything bottled up for the rest of my life. Of course, if that's what I have to do, I'd rather be dead. (No, I'm not suicidal... I just think the peace of being dead would be preferable to enduring this for the next who knows how many years.)
So, I feel for you, man. This cult is responsible for this for way too many families.