Save combobox entries to textfile

I have a combobox that i want to save to a textfile when clicking a button, it should append all entries to a new line UNLESS it already exists. I have the below code, but it doesnt save, it doesnt do anything, but no errors.

   Dim content(TextBox1.Items.Count - 1) As String
        TextBox1.Items.CopyTo(content, 0)
        IO.File.WriteAllLines("C:\SWDEPOT\test.txt", content)

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If a prepopulate the textfile with entries i am able to load it completely fine with the below code:

Dim load() As String = IO.File.ReadAllLines("C:\SWDEPOT\test.txt")
        Array.Reverse(load)
        TextBox1.Items.AddRange(load)

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