While we were still together he took pictures while I was asleep, he never had my permission and is now posting them on soft porn sites and pretending to be me, responding to men who think they are talking to me. Its sick. He has it set as his myspace picture too. What can I do to stop him
You will need a lawyer's help here, unfortunately. You have a right to have these photos removed, but it will require good knowledge of Internet-related law and probably matrimonial law, as well as judgment and experience in dealing with delicate situations such as this one.
This is a very unfortunate situation. You should consult with a local attorney immediately to determine whether the following legal avenues/arguments are available to you.
Defamation: Did the postings to the site make some FACTUAL or APPARENTLY FACTUAL claim about you that is UNTRUE? If so, that might be an avenue of attack.
Right of Publicity/Invasion of Privacy: You should see what your state's (and the state the site operates in) law says about the right of a party to control the use of their own image or to be private. The photo of you might infringe upon these rights.
What the next steps would likely be is an attorney demand letter that calls for take-down and retraction, under threat of legal action.
I hope this helps.
Disclaimer: This answer is for informational purposes only and does not constitute general or specific legal advice, nor create an attorney client relationship.