Splitting a full name string into First, Last and Middle Initial in VBA Access

Names are formatted as a string in [lastName, firstName middleInitial].

I have three text boxes that are labeled lastName firstName and middleInitial.

The code should separate that string into the three boxes but it gets hung up on:
-the first name, where it doesn't stop at the space or it cuts off a few characters
-the middle initial, where it works if they have a middle initial, but throws an error if it doesn't find one.

Private Sub cbxMbr_AfterUpdate()

    If Not Me.opgMngRoster.Value = 1 Then
        'Member's Last Name
        Dim lastName As String
        lastName = Left(cbxMbr.Text, (InStr(1, cbxMbr.Text, ",") - 1))
        Me.txtLastName.Value = lastName
        
        'Member's First Name
        Dim firstName As String
        firstName = Mid(cbxMbr.Text, InStr(1, cbxMbr.Text, " "), (Len(cbxMbr.Text) - InStr(1, cbxMbr.Text, " ")))
        Me.txtFirstName.Value = firstName
        
        'Member's Middle Initial
        Dim midName As String
        midName = Mid(cbxMbr.Text, InStr(InStr(1, cbxMbr.Text, " ") + 1, cbxMbr.Text, " "))
        
        If midName = vbNullString Then
            Me.txtMidInit.Value = " "
        Else
            Me.txtMidInit.Value = midName
        'DoCmd.RunSQL "SELECT MEMBER ROSTER WHERE "
        End If
    End If

End Sub

You can use Split:

' "Duck, Donald D."
' "Duck, Donald"

Me!txtLastName.Value = Split(Me!cbxMbr.Value, ",")(0)
' Duck

Me!txtFirstName.Value = Split(Trim(Split(Me!cbxMbr.Value, ",")(1)), " ")(0)
' Donald

Me.txtMidtInit.Value = Split(Trim(Split(Me!cbxMbr.Value, ",")(1)) & " ", " ")(1)
 ' D. or zero-length string.