Your fiancé needs to retain an experience criminal defense attorney immediately. The attorney will represent him at the preliminary hearing and attempt to resolve the case there. If the charges are dismissed, your fiancé will be able to have the case expunged from his record.
Mr. Keller is exactly right. Your fiance needs the assistance of qualified criminal defense counsel. Urge your fiance to at least speak privately with one or more suitable candidates. Most here will provide a limited free consultation. Since the police obviously ignored your wishes in this matter, it is going to require defense counsel to resolve this in a favorable fashion. Good luck.
Once again, Mr. Keller and Mr. Jones have it right. Strongly encourage your fiance to retain an experienced criminal defense attorney. If he cannot afford private counsel, your fiance should contact the public defender's office right away. Once the legal matter is resolved, both you and your fiance should also make an appointment with an anger management specialist.