inserting a return in text

I've been fighting with this code for a few days now, so now I'll ask....
The attached code checks each line of a rich text box for the word private (when I press return), if it finds it it changes its color and proceeds. Unfortunately, if you have typed out text and are editing that text I cannot insert a line in the middle of the document, instead it forces the cursor to the bottom of the document and inserts the return there.
Anyone want to have a go at this?

Private Sub HighlightText(sKeyword As String, iColour As Long)
Dim nStart As Integer, sPrevChar As String, sNextChar As String

nStart = InStr(1, LCase(TextBox1.Text), sKeyword)

Do While nStart <> 0
If nStart > 1 Then
sPrevChar = Mid$(TextBox1.Text, nStart - 1, 1)
Else
sPrevChar = " "
End If

If Len(TextBox1.Text) >= nStart + Len(sKeyword) Then
sNextChar = Mid$(TextBox1.Text, nStart + Len(sKeyword), 1)
Else
sNextChar = " "
End If

If (sPrevChar = Chr(32) Or sPrevChar = Chr(13) Or _
sPrevChar = Chr(10) Or sPrevChar = Chr(9)) And _
(sNextChar = Chr(32) Or sNextChar = Chr(13) Or _
sNextChar = Chr(10) Or sNextChar = Chr(9)) Then
'If word is from lowercase list then lowercase highlight word.
If lowercase = True Then
With TextBox1
.SelStart = nStart - 1
.SelLength = Len(sKeyword)
.SelColor = iColour
'Sets all text of selected word to lowercase.
.SelText = StrConv(sKeyword, vbLowerCase)
.SelStart = Len(TextBox1.Text)
.SelColor = iColour
End With
'Else propercase the highlightword.
Else:
With TextBox1
.SelStart = nStart - 1
.SelLength = Len(sKeyword)
.SelColor = iColour
'Sets all text of selected word to lowercase.
.SelText = StrConv(sKeyword, vbProperCase)
.SelStart = Len(TextBox1.Text)
.SelColor = iColour
End With
End If
End If

nStart = InStr(nStart + Len(sKeyword), LCase(TextBox1.Text), sKeyword)
Loop

End Sub
Private Sub TextBox1_KeyPress(KeyAscii As Integer)
If KeyAscii = vbKeyReturn Then
With TextBox1
.SelLength = Len(.Text)
.SelColor = vbBlack
If .SelStart = Len(.Text) Then
'If at the end insert a return.
.SelStart = Len(.Text)
Else:
''''''''If not at the end insert return at present location.
End If
End With
'Run highlight script.
HighlightText "private sub", vbBlue
'Reset text.
TextBox1.SelColor = vbBlack
End If
End Sub