He is the only one that can control that timeline. You have to remember that you didn't break him, therefore you can't fix him, nor can you control the length of time is required for him to figure himself out. I, personally, do not like to reference statistics because we can only say what we see here and what the "experts" write about IRL. However, if given enough time and space, you have a 50/50 chance of him waking himself up and realizing that the grass isn't greener on the other side. Now, you have to also consider that after a period of time and you've adjusted to living your own life and rediscovering the person that you were long ago, you may just opt not to take him back. Many come to realize that once they have rediscovered the person that they put up on a shelf to marry the spouse, and they like that former person, they just might decide that they would prefer to venture forth into the future on their own or meet up w/someone much, much better suited to the new and improved self. I've seen that happen many times over both here and IRL.
You really do need to stop discussing the future and the relationship w/him. Right now, he's trying to find that much needed space to figure himself out. The more you discuss the relationship w/him, the more his attention isn't focused on him and why he feels the way that he does. Trust me, the more you push for answers, the less you will get in the way of responses.
We provide the same advice to both the WAS and the MLCer...time, space and no relationship talks. You need to keep the focus on you and what you need to do to improve those areas of your "self" that you think need improvement. Improvements are to be made for you and not to try to win him back. Also, really listen to what he says. You can sift through the comments and you might discover some helpful tidbits.
Again, no relationship talks, stop pushing for answers...he can't provide them right now, focus on you and most importantly dig deeper for patience. This is not a sprint...but a marathon and it will take as long as it takes for him to realize that the grass isn't greener over on the other side of the fence. The more determined he will be to run the other way.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
