"After months of thinking, deliberating, and soul-searching, the time has come for me to make a big decision. How do I work up the courage to say something one way or another and stop the dithering?"
I think we dither when we aren’t ready yet. If dithering is happening, I see that as a sign that the big decision isn’t actually made yet – more time is necessary. Maybe it’s time for less thinking and deliberating and soul-searching, and more percolating and breathing and just plain waiting for clarity. It’s possible, I think, to focus in too tightly on a problem. Maybe backing off a bit will help you figure out what you want to say as well as how to say what you want to say in such a way that working up courage will become unnecessary.
Of course, it’s also possible that courage is necessary because what is right and good for you directly conflicts with what you believe is right and good for the people you’re afraid to talk with. If that’s the case, waiting a bit might still be useful because it might help you figure out what your fears are so that you can address those fears without hurting the other person. The danger here is that waiting, if you are truly clear about what you’re wanting, might end up hurting the other person even more, since (assuming this is something they will have to find out about eventually) waiting will add deception to an already difficult situation. You know what I mean… “You’ve known this since then and you’re only just now telling me???!!!” If that’s the case, then reminding yourself that you’re causing more pain by waiting than by being honest right now might help you gather the courage you require.
I hope something here helps, although I realize that with my long delay in replying to your question you are probably all done dithering…