store username in textbox in Outlook form

[lOOpi]

Hi All
Situation: I am composing an Outlook form with textfield in which I would like to store usernames of users that edit the form (form has other textfields that are completed by users).
I would like the textfield to look like this:

Username ---> Username ---> Username ---> etc.

You can think of it as of approval flow.

Problem:
Only first username is stored - when I open the form and send it to another user he sees me in textbox but when he edits the form and forwards it to someone else he is not seen in textbox, only me (the orgiginator).

Code:
Here is the code I used to accomplish this:

Function Item_send()
    Set MyPage = Item.GetInspector.ModifiedFormPages("P.2")
    MyPage.Controls("TextBox20").value = TextBox20 & " ---> " & Application.GetNamespace("MAPI").CurrentUser
End Function

As far as I know it should be called every time the message/form is sent, but it seems to run only once - when you send the form for first time, therefore only the originator username is stored in textfield.
Any ideas what could be the problem here?