Never
Near would never be L. At least he would never be L Lawliet. Yagami Raito knew this, and he didn't care.
Raito would never be Mello. Near knew this too, he didn't care either.
Sometimes
Sometimes though, the way Raito's eyes slanted, or the way his hair fell when he forgot to cut it; was enough for Near to pretend.
This also went for Raito, Near's hair wasn't black, Near didn't love sweets, Near didn't think the way L did. Yet this was enough, for Raito himself to pretend.
Wrong names
The names were always wrong. L, Mello, those weren't their names. They always refused to call the other by their name; but neither cared.
Lost sanity
At this point, they both knew they were no longer sane.
It never bothered Raito that he was together with the one trying to capture him. Near never had enough evidence, it was safe.
To Near it didn't matter much anymore, he had lost his favorite piece of the game.
Not enough
Raito never had L, he never would.
Near never had Mello, he never could.
They both knew the other was not enough; would never be enough.
They both knew the other was a terrible replacement for the one's they loved, and that they would never get better.
Yet their other, was the only thing they had left.