He should finish his studies and then hopefully find a good longterm job and then reapply after having been in the job for 6-12+ months. There is no easy short term solution. He can also apply for judicial review of the refusal. It is expensive, may not change result and will take at least 1+ years for case to be heard so won’t make a difference when it comes to attending your wedding. You may want to reach out to your MP to see if they can provide any help to you. Won’t guarantee a change in the outcome of the TRV but that is your best option at this point.