There are a couple possibilities here:
1) He really does want to work it out, but he doesn't know how to talk with you about it in a way that feels safe. In this situation I would find a good counselor (I can recommend an excellent one if you are in the Twin Cities) who will help the 2 of you communicate in a safe zone and help you develop the communication skills necessary to continue this marriage successfully. Many men shy away from seeing a marriage counselor because they figure it will just be session with 2 people beating up on them verbally. But if you approach it something like this maybe it will work. "______, you have told me that you need space to figure out if this marriage will work and I respect that. However, I also think that getting a chance to talk through your concerns with me could help. I am guessing that you don't feel comfortable or safe doing that right now with just the 2 of us because we just end up fighting, yelling, etc. But I have heard of this wonderful counselor that comes highly recommended by a number of husbands as a great mediator for these types of discussions (pm for for her name if you want, she saved my marriage from disaster and my husband's best friend's marriage). Would you be willing to attend a few sessions with me?"
2) He really is not interested in saving the marriage but doesn't want the drama and finality of a divorce. In this situation, he will refuse any opportunity for the 2 of you to work on your relationship together. But he will cruelly keep you "hanging on" and waiting for him to come back, because then he feels in control of a scary situation. In this situation, you need to look out for yourself and start divorce procedures so that you can start to move forward.
Good luck and big hugs.