Welcome to the board and congratulations on your upcoming wedding!
Being fairly new here myself, I can't direct you to any threads. I will say that after reading the posts here you are getting good advice.
The only thing I would add is that your fiance, as has been mentioned previously, is going through a grieving process. Going through my own right now with regard to JWs, as well as having gone through some loss grief in the past few years, I will tell you one valuable thing I learned. It is really really really important to honour his timing and to give him the space to do what he needs to do in the time he needs to do it. You say it's been 6 years, but he's still dealing with some relationship issues...this is quite normal, especially if he was raised as a witness, and has family still 'in'.
I know that your wedding date makes perfect sense to you to be a pivotal "new start"; and in a perfect world it would be. I've learned (the hard way) that grief isn't so neat and tidy. If he's indicating that he will deal with it after the wedding, then it's important to let him do so; otherwise if you push (which it doesn't sound like you're the type to anyway), he may end up blaming you down the line.
I have had many well-meaning people try to push me through the grieving stages...it's natural for people who love someone to want them to get through it and feel better again. Unfortunately, grief is a fairly solo activity. It sounds like he's ready to act and let his family know that he has no intention of ever coming back, and thus gain some closure. Just hang on to that and let him know that you're loving and supporting him throughout.
And if I sound wise (hah), it's because I have a wonderful boyfriend who is basically doing that with me. Not pushing me, not directing me, just letting me deal in my own time and reassuring me that he's here. And having such a safe place to heal in is vastly different from doing it in a vacuum.
Welcome again! :)