Can't Remove Public ADO Connection

I have a VBA application that uses data from a sheet in the excel workbook. It accesses this data with an ADO connection. On workbook open I open this connection--I declare it as public variable so I can continue to use it throughout the session. My problem is that the connection really doesn't ever dissappear. I have the problem that once I close the workbook, the project still exists in the VB Editor. How do I get rid of the connection? I am stuck because I declared it as public? I want to keep it open, rather than opening every time I want to use it, because it is faster to keep the connection open.

My code is below.

Option Explicit 'requires variable declaration
'declare global connection
Public cn As ADODB.Connection

Sub OpenDBConnection()
'open db connection
'this happens on workbook open
If cn Is Nothing Then
Set cn = New ADODB.Connection
With cn
.Provider = "Microsoft.Jet.OLEDB.4.0"
.ConnectionString = "Data Source=" & WCHSBook.FullName & ";" & _
"Extended Properties=""Excel 8.0;HDR=Yes;"""
.Open
End With
End If
End Sub