Donna:
I don't post here much any more but your post really hit home for me.
I have no advice about the telling - just that I TOTALLY botched it. I'm not going to get into details here, but it ended up getting really ugly just because I didn't have the courage to say the words. In retrospect, that would have been the best thing to do, for all parties concerned. But like you, I was scared, I was worried, I was riddled with anxiety, and people kept telling me to "hang in there" and "you're married forever" and all kinds of other TOTALLY UNHELPFUL things that didn't do anything but make me second-guess myself.
Anyway, good luck with that.
My other point is this: you should also at least have some idea beforehand of what you want the AFTER to look like. Do you want to keep your house? Or do you want him to keep it? Do you have other property and how do you want that split, etc.? The reason I say this is you don't know how he's going to respond, and you're going to feel guilty, and that's the time you need to be strongest and not allow guilt to sway your decision-making process. If you've already thought through how you want to split things, you'll have those words to fall back on, and won't be so easily corraled into an agreement that doesn't meet your needs.
((hugs)) If you PM me, I'll send you my email address if you want to talk. I know it's going to be tough, but in the end it is so worth it. (And for my EX, too; he got remarried this year to a woman who is really much better suited to him than I ever was. They're really happy together, which makes me feel much better about things.)
Marie