Star Trek Fic Finder

Found it. But it looks like everyone else too. :)

Because yes, it is Atlas (http://www.fanfiction.net/s/5344838/1). The cliffhanger of Chapter 21 (http://www.fanfiction.net/s/5344838/21) to be precise:

No! Spock screamed, racing after the last fading echo of Jim's lifeforce. It slid through his fingers even as the body of his only, perfect fit stuttered and strained and then grew still. Jim Jim Jim, Spock's mind wailed, twisting useless seeking circles in the empty mindscape, trying to fill it with his own memories and fear and love. T'hy'la Jim don't go Captain stay Jim Jim no

And No! the Other echoed, horrified realization ringing across the vast darkness. Oh no, no! Trickery! What have we done?

Jim Jim Jim, Spock begged, frantic and lost. Jim Jim Jim

There was nothing.

Jim Jim Jim.

There was nothing.

Jim.

But there was nothing.

What have we done?