Как найти конец слова?

    
 Dim list_str As New List(Of String)
        list_str = TextBox1.Text.Split(" ").ToList
        Dim len_start As Integer = 0
        For Each elem As String In list_str
            If elem.Contains(TextBox2.Text) Then
                TextBox1.Focus()
                TextBox1.SelectionStart = len_start
                TextBox1.SelectionLength = elem.Length
            Else
                len_start += elem.Length
                len_start += 1 ' на каждый пробел
            End If
        Next

 Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click
        txt = RichTextBox1.Text
        nm = InStr(poz, RichTextBox1.Text, TextBox1.Text)
1:
        If nm > 0 Then
            str = Mid(txt, nm, Len(TextBox1.Text) + 1)
            If str.Contains(" ") Then
                RichTextBox1.SelectionStart = nm
            Else
                nm = nm - 1
                GoTo 1
            End If
            stw = Microsoft.VisualBasic.Right(txt, Len(txt) - nm + 1)
            nmt = InStr(1, Trim(stw), " ")
            RichTextBox1.SelectionLength = nmt - 1
            RichTextBox1.SelectionBackColor = Color.LightGray
            RichTextBox1.SelectionColor = Color.Red
            RichTextBox1.SelectionFont = New Font("Verdana", 12, FontStyle.Bold)
            poz = nm + nmt
        Else
            Exit Sub
        End If
        nm = InStr(poz, RichTextBox1.Text, TextBox1.Text)
        GoTo 1
    End Sub

Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
    Dim fs As String = TextBox1.Text
    Dim qq = From q As String In rtb.Text.Split({Chr(32)}, StringSplitOptions.RemoveEmptyEntries) Where q.StartsWith(fs, True, CultureInfo.CurrentCulture)
    If qq.Count > 0 Then
        qq = qq.Distinct
        Dim idx, k As Integer
        For Each s As String In qq
            idx = 0
            Do While idx < rtb.Text.Length
                k = rtb.Find(s, idx, RichTextBoxFinds.WholeWord)
                If k < 0 Then Continue For
                rtb.Select(k, s.Length)
                rtb.SelectionBackColor = Color.LightGreen
                idx = k + s.Length + 1
            Loop
        Next
    End If
End Sub

   
Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
        Dim len_start As Integer = 0
        For Each line In RichTextBox1.Lines
 
            Dim arr As List(Of String) = Split(line, " ").ToList
            For Each word In arr
                Dim searh_word As String = LCase(word)
                If searh_word.Contains(LCase(TextBox2.Text)) Then
                    RichTextBox1.Select(len_start, word.Length)
                    RichTextBox1.SelectionBackColor = Color.LightGreen
                End If
                len_start += word.Length
                len_start += 1
            Next
 
        Next
    End Sub

  Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click
        t = {"(\b", LCase(TextBox1.Text), ")\b"}
        Pattern = String.Join("\w*", t) & "\w*"
        Application.DoEvents()
        Dim Group1 As String() = (From M As Match In Regex.Matches(RichTextBox1.Text, Pattern) Select M.Groups(0).Value).ToArray()
        '[  
        For i = 0 To Group1.Count - 1
            Dim allIp As MatchCollection = Regex.Matches(RichTextBox1.Text, Group1(i))  ' Word)
            For Each ip In allIp
                RichTextBox1.SelectionStart = ip.Index
                RichTextBox1.SelectionLength = ip.Length
                RichTextBox1.SelectionBackColor = Color.LightGray
                RichTextBox1.SelectionColor = Color.Red
                RichTextBox1.SelectionFont = New Font("Verdana", 12, FontStyle.Bold)
            Next
        Next
    End Sub

  Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click
        RichTextBox1.Select(1, RichTextBox1.TextLength)
        RichTextBox1.Select()
        RichTextBox1.SelectionColor = Color.Black
        RichTextBox1.SelectionFont = New Font("Verdana", 10, FontStyle.Regular)
        t = {"(\b", TextBox1.Text, ")\b"}
        Pattern = String.Join("\w*", t) & "\w*"
        Application.DoEvents()
        Dim Group1 As String() = (From M As Match In Regex.Matches(LCase(RichTextBox1.Text), Pattern) Select M.Groups(0).Value).ToArray()
        '[  
        For i = 0 To Group1.Count - 1
            Dim allIp As MatchCollection = Regex.Matches(LCase(RichTextBox1.Text), Group1(i))  ' Word)
            For Each ip In allIp
                RichTextBox1.SelectionStart = ip.Index
                RichTextBox1.SelectionLength = ip.Length
                RichTextBox1.SelectionBackColor = Color.LightGray
                RichTextBox1.SelectionColor = Color.Red
                RichTextBox1.SelectionFont = New Font("Verdana", 12, FontStyle.Bold)
            Next
        Next
        RichTextBox1.Focus()
    End Sub

Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click
    RichTextBox1.SelectAll()
    RichTextBox1.SelectionColor = Color.Black
    RichTextBox1.SelectionFont = New Font("Verdana", 10, FontStyle.Regular)
    Dim Pattern = "(\b\w*" & TextBox1.Text.ToLower & "\w*)\b\w*"
    Dim mm = Regex.Matches(LCase(RichTextBox1.Text), Pattern)
    For i = 0 To mm.Count - 1
        RichTextBox1.SelectionStart = mm(i).Index
        RichTextBox1.SelectionLength = mm(i).Length
        RichTextBox1.SelectionBackColor = Color.LightGray
        RichTextBox1.SelectionColor = Color.Red
        RichTextBox1.SelectionFont = New Font("Verdana", 12, FontStyle.Bold)
    Next
End Sub

Private Sub Button5_Click(sender As System.Object, e As System.EventArgs) Handles Button5.Click
    Dim Pattern = "(\b" & TextBox1.Text.ToLower & "\w*)\b\w*"
    Dim mm = Regex.Matches(LCase(rtb.Text), Pattern)
    For i = 0 To mm.Count - 1
        rtb.SelectionStart = mm(i).Index
        rtb.SelectionLength = mm(i).Length
        rtb.SelectionBackColor = Color.LightGray
    Next
End Sub

Private Sub Button6_Click(sender As System.Object, e As System.EventArgs) Handles Button6.Click
    rtb.SelectAll()
    rtb.SelectionBackColor = rtb.BackColor
    rtb.DeselectAll()
End Sub