Darkness. For one Gin Ichimaru, darkness meant safety. It meant that he would finally be left alone, that they wouldn't come and bother him. The darker, the better.
He knew that they tried. They truly did. And sometimes, they helped. But despite all of that, and despite the fact that Tesla had gone through something similar, it was still nothing like the hell that he had endured. And because of that, they could never really understand. Which made it that much harder to help him. But still, they tried.
He had gotten better. So very much better. He no longer became startled at the smallest of sudden noises, or the sound of yelling. The slightest touch to his wrists or neck, even from his own clothing, no longer made him hyperventilate out of fear that his chains were back.
Despite that, he was still broken. Broken past the point of repair. If a bowl is shattered into thousands of pieces, you can try to glue it all together. But there is still some missing, and it is still broken. It's just held together, long enough to function. They were his glue, much like Rangiku had been.
When he first arrived in Hueco Mundo and realized that he left Rangiku behind for good, he couldn't help but feel like it was a mistake. The glue that held him together was washed away, leaving him broken into thousands of tiny pieces that would be swept away in the next breeze, or the next wave. He only did what he had to, to complete his mission. Then he would get rid of himself, so that he would no longer be afraid. No longer hurt. Because he was no longer being held together by his glue, and was broken.
Then he met Tesla. Tesla, a man who was broken like himself. But not nearly as broken. Tesla had only been broken into a few large pieces, nothing like the dust Gin had been shattered into. And Tesla still had his glue, that being in the form of one Nnoitra Gilga. He could tell that Tesla was not in any danger of coming apart any time soon. His glue would see to that. But Gin was still broken.
Tesla tried to grow close. For some reason, Gin let him. They grew closer, and Gin stopped feeling so broken. But he still was, and he still didn't have any glue strong enough to hold him together. So Tesla shared his glue with Gin, and Gin wasn't at risk of being swept away anymore, he was being held together.
They were his glue, the things holding him together. He loved them for it, sometimes. And sometimes, he hated them. He was always hurting, always afraid. Darkness was the only thing that still brought comfort. On the good days, he could lose himself in Nnoitra's hair color, and imagine it wrapped around him and that would be enough. But it wasn't always. Sometimes he had to go under the bed, or lock himself into the closet in an attempt to get that darkness he craved.
On the worst of days, he hid in his inner world. There, it was dark everywhere. So dark and cold, just like how he liked it. He would curl up with Shinsou, and he would finally feel safe, if only for a little while. But he would always have to come out, eventually.
He was broken, but they were the glue that held him together. He just hoped that this time, he wouldn't have to leave his glue behind. He wouldn't survive it.