Failing to provide medical treatment to an inmate is one of the few exceptions to the California laws that immunize the state from liability for injuries to prisoners, so your boyfriend might have a lawsuit against the state. That has to be pursued within six months though by filing a claim, so if he was hurt he needs to contact an attorney soon.
If your boyfriend has suffered any damages as a result of being refused treatment, then he might have an Eighth Amendment deliberate indifference claim. Now, whether or not he is still in jail will determine how any potential claim would be pursued. (For example, if he is still an inmate, then he is going to have to satisfy the PLRA (Prison Litigation Reform Act) exhaustion requirement before filing any kind of a lawsuit against the county--that is, he needs to file an administrative grievance first.)
Ms. Berjis is licensed to practice law in the State of California. The laws of your jurisdiction may differ and thus this answer is for informational and educational purposes only and is not to be considered as legal advice. Since all facts are not addressed in the question, this answer could change depending on other significant and important facts. This answer in no way constitutes an attorney-client relationship.