I have bi-polar disorder and I have withdrawn from my family and everyone that is close to me.

I had the same experience when I was first diagnosed with Bipolar Disorder 2 years ago, I just totally isolated myself from everyone and everything.  I allowed limited interactions with close family but it wasn't in the same capacity as before. It's like a cord just snapped or maybe it was like I was pulled out of the socket and could not be in the same network as them anymore.  It hasn't been the same since.  I have increasingly spent a huge amount of time isolated and alone - but I did get a pet dog and it really helped.  Even if I could not relate with human beings, at least having a pet really helped. 

 It is near impossible for me to open up as well.  I have had a few attempts at trying to open up but it ends with retreating back into a shell and staying there.  I guess it's a work in progress for all of us.  Being able to acknowledge the isolation chamber where we find ourselves is already the first step, I suppose. 

Are you also recieving psychotherapy?  If not, you should be!  Some people are against it but Bipolar II can be controled with a little effort and that doesn't mean you have to give up your defenses right now.  If you feel you need these defenses to protect yourself, then you should maintain them but you will need to learn to accept others into your world in order to keep them in your life.  Sometimes that learned behavior must come through therapy.  Sounds like you were devastated by the diagnosis and maybe a bit fearful of what it would mean to those around you.  Start out small by talking about your feelings and fears about having bipolar to your husband.  It will help a great deal for you to share that with him.  It wouldn't hurt to take him with you to the doctor or the psychotherapist.  In fact it could help him feel that you are trying to draw him into your world without you having to let your walls down just yet.  Don't block him from understanding what you're going through.  He may well be more supportive than you think and that could in turn help you let him in further.

 Good luck!