First of all, stop talking to him about his case on the phone and at visiting. When you hear that voice that says the calls can be recorded, they aren't kidding, and I've never seen a case where those jail calls helped the client.
It's absolutely impossible to give you a meaningful answer without knowing the exact charges involved. He could be looking at substantial time in prison for the charges and gang enhancement; if he's served prior prison terms, he could be looking at additional time for those, too.
A single prior prison term could add a year to the potential sentence. If his prior convictions are for felonies listed under the Three Strikes law, his sentence could be doubled, and this could possibly turn into a 25-life case.
It will be easier to determine the possible sentence once the DA files charges. His attorney -- whether it's someone he hires or a court appointed public defender -- will have a clear picture of the case than a stranger on the internet who has only minimal information
Please understand that this is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. It's impossible to give detailed, accurate advice based on a few sentences on a website (and you shouldn't provide too much specific information about your legal matter on a public forum like this site, anyway). You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information.
By now, I am sure you are aware that your boyfriend is facing extremely serious charges with potential state prison time. He could be facing a parole violation.
Nobody here can tell you for certain what he get--only the attorney handling his case would know, because that attorney would have all the evidence, and understand the strengths and weaknesses of his case. If you have not done so already, consult with a criminal defense attorney, and consider retaining one who is experienced in these matters.