Git Commit after merge opens VIM

Git is opening vim because your environment variable EDITOR is set to vim, and Git believes you need to provide a commit message for the merge operation, therefore it is opening an editor for you to type one in.

You can fix this by changing your environment's EDITOR variable to something you prefer, or by providing a --message "this is my commit message" argument after git merge -y

If what you want is to perform the merge and avoid opening any text editor, you can add --no-edit to your merge command so that it won't open the editor for the commit message.