[9S understands what 2B is suggesting, or at least he thinks so. He was free of the limitations YoRHa had imposed upon him, free of a cycle of death and restriction that had defined his short and violent life. And yet free of these confining factors, free of his increasingly unwilling executioner, what did 9S have? So much of his identity, so much of his sense of purpose, was tied to YoRHa, and the lie they were created to unknowingly perpetuate.

Divested of that purpose, his new purpose had become supporting 2B. And 9S was satisfied with that much, despite the role he was certain she had in his life. There is no denying he felt betrayed and hurt, suspecting that she had killed him time and again and that his memory was tampered with, but in the end...

In the end he still wanted simply to love her. And Adam had seen that contradiction within him, resenting and loving someone at the same time, mocked and derided him for it, echoing some of the thoughts he already directed at himself for the same.

But the same reason he struggled to reconcile those emotions is the same reason he doesn't want to exist without her]

You were always my world, 2B.

[9S remembers distinctly what it is to be alone. He didn't need a reminder in the form of her death and consequent absence from his life. In the past he had chosen to end himself rather than her, to perpetuate (selfishly) the cycle of meeting her and dying at her ever more grudging hands. Because each of those deaths still came with the promise of meeting her again]

It was enough for me, just being at your side. We might not have families, the way humans do, but I... [He trails off, line of sight sinking to the sand] To me, that's what you are.

[So what was left for him without a purpose, without a home, and without her?]