I have payed for my own copy of LTU, but before I did I ran a pirated copy and also referred my friend to the same pirated copy. He no longer uses LTU, but do I have to buy a new copy of LTU to disable the protection?
No you pay for your own copy plus your friend doesn't use it anymore. Otherwise people who has shared on torrent would have to pay for all the guys they shared which would be impossible.