I think he may have been shown the files on his former comrades just as was Locke.

And, now Jack sees them in a different light, just as does Locke.

He has lost that common bond he had with the rest of the Losties because they all ended up either lying or misrepresenting their circumstances. He feels alienated and alone

Since he no longer feels a kindred bond with them, he is spending more time with the ONLY one on the Island that he perceives has endured a similar alienation or mistreatment -- Juliet.

Misery loves company.