For a Multiselect control you need to look at each index to see if it is Selected.
This is just example code, It doesn't actually fit your requirements.
Private Sub LBox1_Exit(ByVal Cancel As MSForms.ReturnBoolean)
Dim i
Dim j
Dim SelectionList(lbox1.ListCount) 'an array of selected Items
Dim Selections As String 'A comma separated String of Selected Items
For i = -1 To lbox1.ListCount - 1
'List indexes start at zero, Counts start at 1, Listindex -1 means no item selected.
If lbox1(i).Selected Then
SelectionList(j) = lbox1(i)
j = j + 1
If i = -1 Then
Selections = "False"
Else
Selections = Selections & ", " & lbox1(i)
End If
End If
Next i
End Sub