1. First of all use CODE tags instead of QUOTE - it's difficult to get through your pasted code now...
2. What I can see is that when you want to show next part of output you are appending existing text plus new text. So it looks like this:
You have this in your textEdit
some text
and you get from the output string "some different text", Now you are getting the old "some text" adding "some different text" to it and than appending (adding to the end) it to textEdit. The result is:
some text
some text
some different text
instead of:
some text
some different text
Append means "add to the end" so you can just append new portion of text without copying existing text one more time.