dudycat1 said:
well he just realized that i wasn't going to give in to his demands so he decided to post the video on the internet, now all i need to do is find a cheap lawyer.......
You don't need a cheap lawyer, you need a competent lawyer who will recover their fees from the guilty party (or Criminal Compensation Board) after they defeat them in court.
Assuming you're in the UK, you should probably contact the Crown Prosecution Service because as well as the aforementioned blackmail attempts, the watching of the sex tape without your consent constitutes as Voyeurism, which is criminalised under the 2003 Sexual Offences Act and could possibly lead to charges being levied against the website hosting the sex tape.
http://www.cps.gov.uk/news/fact_sheets/sexual_offences/
http://www.cps.gov.uk/legal/s_to_u/sexual_offences_act/
Those links would be a good place to start, as you know more about your own situation than you've disclosed, so you may see other sections of the act that may be applicable.
For example, if you have a recognised mental disorder you could be classed as a vulnerable adult, or if one of your friends or family that he's threatened to send the links of the sex tape to is below the age of consent, then that could be classified as "forcing a child to view a sexual act", which could land him in a whole heap of trouble.
Anyway best of luck to you whatever you decide to do, but I do think it would be best to contact the Police and/or CPS before a contacting a private lawyer, as this is a lot more serious than just a private, civil disagreement.