Add cell values to a TextBox

[BasicUserWithExp]

I have a bid form and in column R there is a predefined list of items, and in column S there is a predefined list of reasons. I would like a way to populate a TexBox with those values
Example:
R37 = Spread Footings; S37 = Blank
R38 = Grade beams; S38 = GB1-10

I would like code to then put the values in a TexBox like:

Spread Footings, Grade Beams - GB1-10,

I have a way to do it now, using CheckBoxes and it works, but when i add rows above it I have to change the code every time:

Private Sub CommandButton1_Click()


TextBox1.Text = ""

If CheckBox1.Value = True Then
    TextBox1.Text = TextBox1.Text & Range("R28").Value & " - " & Range("S28").Value & ", "
End If...

can code be created for a range? R28 to R50, and Double Click corresponding cell in column P to add?

If the same code could clear the TextBox prior to adding values, or separate code/button That would be great!