First and foremost, thank you for choosing justanswer.com. I am a licensed criminal defense attorney, former Deputy District Attorney, and member of the American Bar Association.
The District Attorney's Office cannot proceed with their case if they do not have a witness; you can refuse to be a witness in the case if you have decided a criminal prosecution is not "what the doctor ordered". The DA's would be unable to proceed with a case against your ex-boyfriend because of the amount of time that has elapsed, the lack (or absence) of physical evidence, and absent your testimony.
The first thing you should try is calling the Assistant District Attorney assigned to the case and explaining to him/her exactly how you feel and why you feel the way you have described. This often is all that need be done in order to have the charges fully dismissed or at least lowered to the extent of paying a simple fine.
Your other option would be for you to refuse to proceed with the case by not appearing in court if you have already tried the above and the DA's have not been sympathetic to your cause. The DA's will send you subpoenas with nasty language on it demanding you appear in court but almost never take any action against an individual in your situation; the case will simply be dismissed.
I saw this hundreds of times as a prosecutor and it is actually a common occurrence. Cooler heads have prevailed by the time the case got to court and the parties wanted to settle things outside the courtroom; the DA's office complied.
I hope this helps. Please, click accept if you found my answer helpful so I may receive credit for my response. Do not hesitate to contact me via justanswer.com with any further questions or concerns. Thank you and good luck!!