It wasn't a leak.
He let his GF have access to classified material, which went no further.
The GF did not publish or otherwise disseminate the material.
He was a dope, but is being punished for non-security reasons.
Had he wanted to in his capacity as CIA director, he could have given her access and had her sign a non-disclosure. Then it all would have been legal. He might have had a tough time justifying need to know, but had he approached it as the CIA director rather than as a cheating husband, he would have gotten away with it.
But, I think the NSA reported all his communications to Barry and Hillary, so there was no such thing as secrecy in his life. A reminder: everything looks worse in black and white. A face to face conversation is still the best secure means of maintaining confidentiality.
His GF did not have an active security clearance or the damn need to know. The General should be doing time for this period. If I disclosed classified info to my GF regardles of wherter or not she disclosed it, I would lose my clearance, my job, be fined, and go to jail. The General signed the same damn non-discloser agreement I did. He needs to be treated the same as anyone else who broke that trust. His military and tactical prowess do not put him above the law!