Nill can't help but wonder if these are the first things she's really told him about herself. Not that her time in the Arena didn't demonstrate a fair amount, from self-hatred to a complete lack of ability to look after herself closer to the end, before Karkat, before she died. She's spent more of her time hoping he wouldn't notice things about her than hoping he would notice anything about her.

It feels like a long time since she told anyone much about herself at all, and certainly not without the safety of a means of communication that was largely undetectable.

She stares at his hand for a long moment, and then writes hastily on another napkin, sliding it over a little sooner than she might normally. The reason becomes obvious soon enough; while his hand is still closer to her, note written, she reaches to gently clasp his hand in both of hers, looking a little more at his fingers than his face.

I'm grateful too.
I'm really glad you're still here.

She thought he might not be when she was in the Arena. Not that he would know that. It wasn't a concern she could speak out loud, and the only person she expressed it to never said much about it out loud either. But she'd been genuinely worried he might not be here anymore if she made it back.