when does he remember what happened before with her?

There’s still a few chapters. Seeing how short the drawing is, maybe 25 chapters or so. Anyways there’s the novel.
In the novel this last manhwa update is chapter 44.
From chapter 90 something (93 maybe) he starts to remember

chapter 156 is one of the main points


Here:
https://novelbin.com/b/flowers-are-bait/chapter-44