This is a common question on AVVO. If you filmed yourself, then you probably own the copyright to the video. To sue for copyright infringement, you need to register the video with the copyright office. That may sound odd, given the nature of the material, but you can still obtain a copyright registration if you filmed yourself, since you are the creator of the 'work.' Copyright registrations are not expensive - $35. Then, if he posted the video online, you could sue him for damages and attorneys fees. Depending on the law of your state, you may also have the ability to pursue claims for invasion of privacy, and violation of your right of publicity. Those claims do not depend on your copyright ownership. A cease and desist letter to your ex-boyfriend may be enough to prevent the posting of the videos. If either you or he are minors, other legal issues are involved, and you should speak to an attorney in confidence.
Disclaimer: The foregoing does not constitute legal advice or form an attorney/client relationship. Please contact an attorney for formal legal advice on any specific matter.