I've been wondering when this moment would come, but I think you're right. I think Jack has finally said "ENOUGH IS ENOUGH!" He's been instrumental in saving the US time and time again since the show's inception...and at the expense of many of the people he loves. He lost Terri at the end of Day 1, lost his daughter when he "died" at the end of Day 4, and lost Tony and Michelle because of his decision to fake his death.

Not to mention the countless suicide missions he's undertaken at the request of his government. Flying the nuke into the desert in Day 2, going back undercover with the Salazars in Day 3, attacking and illegally detaining a prisoner at the Chinese consulate in Day 4, and agreeing to help divert the crisis in Day 5 (albeit under false pretenses by President Logan.)

He's put his ass on the line long enough.