To open a file relative to the current one in #HelixEditor, you can to the do the following with the current version:
:o <C-r>%<C-w>
Here, the Control-R allows you to select a register and the special register "%" contains the current file path and inserts into the command line, while the final Control-w chops off the last part of the file name leaving with you current directory.
With #Neovim it's a bit shorter:
:o %:h
There, %:h stands for the "Head" of the current file path.
@mushidango It sounds like you are referring to the Vim option “autochdir”. It constantly changes the “current directory”, to match the file, which may not be desirable. Here are the docs for that:
“When on, Vim will change the current working directory whenever you open a file, switch buffers, delete a buffer or open/close a window. It will change to the directory containing the file which was opened or selected. Note: When this option is on some plugins may not work.”