BTW since she was his authorize security cleared biographer she did have clearance.
Read the entire story. Wilipedia gives a good summary.
Yes he did divulge it to the girfriend. And no, she was not cleared to receive compartmentalized classified information.
For example, my Secret clearance does not allow me access for information I do not have a need to know or classifications above the access level. The need to know requirement applies in all classified documents cases. Unless you need to know you have no right to the information regardless of your security clearance.