As long as there is a ember of feeling left in the X, there is hope. Bu t, embers need time to turn into flames. I too, had a moment last summer, before divorce was final and uttered the "I miss you" feeling. Somehow I thought if I told him my feelings he would reciprocate with the same feelings. No such luck! It got worse, and I too felt hopeless. As far as going dark, I am not an expert on that, but I do think you can quickly turn this around with a change of attitude. Yes, they know us, but just like them we too can change. You've got to fake it. With every future interaction, let her get the feeling that the last conversation was the last straw with you, and although you can remain cordial, you are now moving on. I have become a master at disassociating from hi m while conversing, or meeting. I can appear happy, confident and less interested and honestly, the faking alone has contributed to the genuine change I feel. I know he notices. He now engages me in conversation and calls more instead of tx paging. I know I am a long place from where I would like to be, but time is on my side. I know there is a ember somewhere in him, and while he tries on new relationships, I will continue to exercise, read, and stay as busy as possible.
Hang in there. Everyday is a chance for a new beginning.