Just Pixiv at the moment (with some advanced previews on Fanbox). afaik Neji hasn't announced any plans for another tankobon collection, even in Japan.
She is apparently working on another smut doujinshi, though.
I'm betting that Lilly's just talking about something mundane, like being able to go into town or interact with other humans, without her needing to be present to reassure others or calm Keith down, rather than anything big or dramatic like Keith is assuming.
That is, when she says "when I'm not around" she specifically means "when I'm doing something else at the moment or need to be elsewhere," so Keith isn't stuck waiting around for her or planning her schedule based on Lilly's.
I'll bet a hundred bajillion dollars that she is literally just talking about something that will lower Heath's anxiety when they aren't physically together. In fact, I'd bet that she got Heath a ring, which will turn out to be a hilarious coincidence when it turns out Heath got Lily a ring.
Can there be like a law against contrived "oh no a character heard something that sounds bad out of context and now they're misunderstanding things" complications?
The technical term for this is "Sudden Onset Anime", which may be Acute or Chronic (cf. "Idiot Couples who always fight"). Misunderstandings, assumptions, avoidance (sometimes leading to running away), isolation, and Not Just Fucking Talking To Each Other are common symptoms of Anime.
If you think you or someone you know is suffering from Anime, slap them upside the head and tell them to stop being stupid. Anime is a silent epidemic that annoys millions each year and many experts claim it's the worst thing no one has literally died from. (Some historical epidemiologists suggest Romeo and Juliet did suffer from a terminal case of Anime, but records from the time have all been destroyed by families involved in shame over how stupid their kids were.)