using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string text = @"[配送日時指定:]

        2019-03-08(金)

        13時〜14時 (配達担当：野村)

        テスト注文

        [びこー１:]

        備考欄って「注文フォーム」って言]うんですって。

        [asdf:]

        [びこー２:]

        びこー２";   

      string pat=@"\[(.*?)[:]\](\s)";

​

      // Instantiate the regular expression object.

      Regex r = new Regex(pat, RegexOptions.IgnoreCase);

      // Match the regular expression pattern against a text string.

      Match m = r.Match(text);

    int lastIndex=0;

        var lastKey="";

      while (m.Success) 

      {

         for (int i = 1; i <= 1; i++) 

         {

            Group g = m.Groups[1];

            CaptureCollection cc = g.Captures;

             Capture c = cc[0];

             if(lastIndex>0){

                 var strLength=c.Index-c.Length-lastIndex;

                 strLength=strLength==-1?0:strLength;

                 System.Console.WriteLine("Key="+lastKey+" , Val="+text.Substring(lastIndex,strLength));

             }

             lastIndex=c.Index+c.Length+2;

             lastKey=c.Value;

         }

         m = m.NextMatch();

      }

        if(lastIndex>0 && text.Length>lastIndex){

            System.Console.WriteLine( "Key="+lastKey+" , Val="+text.Substring(lastIndex));

        }

    }

}