You still don't seem to be filtering your recordset with a passed in URL parameter. I still don't see how you are linking into the update page to allow the update.
The link to the update page should look something like:
Where the ID of the record to be update is being passed to the update page.
Then the update page recordset should look like:
$termineedit = new WA_MySQLi_RS("termineedit",$aktuelles,1);
$termineedit->setQuery("SELECT * FROM Termine WHERE ID = ?");
$termineedit->bindParam("i", "".(isset($_GET['ID'])?$_GET['ID']:"") ."", "-1"); //colname
So that it uses the ID to show the correct record. The update code looks correct, but it won't work if you don't access the page with an ID in the url to begin with.