Bipolar and getting booted from the AirForce..?

My husband has been in for 8 years and fully functional. He has never been in any serious trouble with the AirForce and has never shown he cannot perform his work duties. He was recently diagnosed with being bi polar and the doctor told him that they will more than likely have to kick him out. Can anyone help me find information on how they can do this? I have seen the regs about bipolar preventing you from joining if it is a preexisting condition..but he has been an upstanding soldier for 8 going on 9 years? Any help or advice on this would be greatly appreciated!!!!