Well, when the browser submits a textfield it uses newlines (\n) to designate a new line... PHP however, since you need to output it as HTML, needs to use <br> HTML tags... SO... What you can do is before entering the data into the database is use this command:
$form_textbox = str_replace("\n","<br>\n",$form_textbox);
and, of course, replacing $form_textbox for the variable your text is in...
Hope this helps 🙂