I need to talk to him but it's so hard!

Um, because you're normal. You can talk all day to other people because they aren't actually part of the problem. Talking to friends about your marital issues? Easy. Talking to the person who's causing you pain? Damn hard. It's always harder to actually deal with an issue than it is to think about it.

Think of it this way - let's say someone has an issue with weight. Is it easier to talk about the things you know should do or go out and do them?

So, you're normal. Yes, it sucks. Yes, it's hard (that's not your imagination). Yes, you will have to FORCE yourself to have this conversation. And yes, you can do it. Breathe deep and jump, girlfriend. You can handle this.

I never found it hard to discuss the dysfunctional issues in my marriage. The 1st talk was a bit 1 sided with me doing all the talking but after 6 or 8 it got like making a sandwich.
I would suggest that you put together a written page addressing exactly how you feel and what you need to see from him in response to your concerns and how you see separation and divorce as the end of the road if things don't change. List the must haves and a realistic time frame for them to come about. Writing things down will hopefully assure you don't become flustered or lose track of where the talk needs to go. And put a date at the top to remind yourself that there is a drop dead date for the changes to come about.
If you really want to hold his feet to the fire add a paragraph at the bottom stating his determination to work toward changing along with a time line. Then have him sign it.

I did the "write it down and practice it" thing and it did help! I also told him, please just listen to everything I have to say and then I will listen to your response. (FYI, this was the "I'm divorcing you" talk, not one of the hundreds of "we need to work on our marriage" talks.)

And this, ggold, is where it needs to go. No more we need to do this or that. That ship has sailed. You're stressing over a talk, but it's not a talk. It's an announcement. I am divorcing you. You will of course listen to what he has to say but the decision has been made. From here on it's a legal matter so you should say as little as possible.

Exactly!!  The fact that I cannot and have not been able to discuss intimate issues with my husband IS a major problem.  Good God!!!!  It pisses me off so much that my stomach gets in knots when I think about talking to him!!  It's ridiculous!  A married couple should NOT have issues with communication.  Period.  

We had issues communicating about sex and intimacy early on in the marriage.  I was young, never spoke my mind, kept feelings inside, and maybe just didn't have the skills then to deal.  Here I am almost 23 fucking years later, and have improved upon myself in many ways but not in the area of communicating w/him!!  Why is this???  What am I afraid of???  Why can't I just get the damn words out??  I know how he's going to react.  It's the same way he always does.  He'll give me his sad face, say he doesn't want a divorce, he won't leave the kids, etc.  

As the attorney I consulted with told me, the only way he will have no choice but to take me seriously is when I retain counsel and get the divorce going.  She is most likely correct.  

I have written him so many letters in the past.  I have two sitting on my dresser right now, just never gave them to him!!  

There is nothing he can do at this point to change.  The damage is done.  I am 100% checked out of this marriage.  He is just now going through his own therapy to deal with whatever his issues are.  I have been in therapy dealing with my grief, sadness, disgust, rejection, etc. from this SM for awhile now.  We tried couples therapy last summer.  It was then I knew for sure there was no hope.  He thought so, though!  

We have three young kids and we need to be there for them.  I just want him to accept that, but he probably never will.  I have to move on anyway.  :-(

I've got a different  approach for you. Since you already know his response, why not make it short and blunt, with very little room for discussion or compromise.

I also think you should retain an attorney first, get that set in stone. By retaining an attorney, funds will be frozen and he will be served within 48 hrs, despite his reaction. Be prepared for months, years to come to say," I asked for the divorce, because,,,blah, blah, blah" you may find that the best response back to him will be, " speak to my attorney". I would not leave your house either, I hope an attorney has advised you on that.

Right now I find the word " divorce" strong, depressing, and painfull.What I plan to say is" I am ending our marriage". That does not mean I am ending my family,or divorcing my family. It means you chose to detach yourself from me years ago, to live with out me, so I am legally ending the marriage, and giving our family and myself a new start.