Your boyfriend should consult with a DUI defense attorney who practices in your area. Depending on the facts in his case as well as the time frame of his plea, it may be possible to withdraw the plea and contest the DUI. Whether that will makes things better or worse is something an attorney can advise during a consultation.
Did your boyfriend request counsel? I would have your boyfriend consult an attorney in the jursidiction where he entered his guilty plea to assess the possibility of withdrawing his guilty plea and the possible benefit and outcomes of doing so.