Richt Text Box with numbered lines

Question

Hi

A few days ago I started developing a little HTML Editor.
I tryed integrating line numbers into it but im not realy lucky right now.

I use the KeyDown event to respond on the Return/Backspace keys then I count the lines and write it into a second RT-box left to the main Editor RT-box but there are some problems with this solution.
Sometimes there are too much or not enough numbers... then I cant find an event for automatic line breaks.
How would you solve this?

my solution:

private void richTextBox1_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyCode == Keys.Enter)
            {
                generateTextLineContext(richTextBox1.Lines.Length);
            }
 
            if (e.KeyCode == Keys.Back)
            {
                generateTextLineContext(richTextBox1.Lines.Length);
            }
        }
 
        private void generateTextLineContext(int lineNumber)
        {
            richTextBox2.ResetText();
            for (int i = 1; i <= lineNumber; i++)
            {
                richTextBox2.Text += i.ToString() + System.Environment.NewLine;
            }  
        }

Thanks!