Sasi,
  He's waffling because he doesn't want to lose his comfy perch with you.  When you leave, he'll have to depend on himself.  He'll have to actually process everything he's been denying to himself, or hiding, or blame shifting onto you.  So of course he's waffling; he doesn't want to face who he is and what he's done to you for so long.  He's got a habit of blaming you ("asexual"; "frigid"), and he's not going to give that up easily, so be prepared for him to blame you for things both old and new.
  As for your sister, tell her exactly what you think of her insensitive comment.  She may not like him, you may be divorcing him, but you've spent years of your life with him, and even though they weren't all good years, you thought they were what they seemed to be.  Now he's knocked all the supporting beams out from under everything, with the result that you're questioning your judgement--if he wasn't who you thought he was, did things happen as you thought they did?  This leaves one crazy and naked, so to speak.  It makes you wonder if anything is what you think it is or thought it was and whether you can say anything for sure.  
   Get a therapist who is schooled in trauma, domestic trauma and abuse, and use her.