"But who will protect you?!"
Alright. Take a look at this scene for a second, because I missed this the first couple times. It’s time for another overanalyzation, shit quality gif accompaniment.
You see in the third gif? Jack says something to North right before Jamie steps up. Jack touched North’s hand, reassuring, and North shakes his head. Jack looks like he’s about to do something, and North doesn’t want him to do it. For a split second, you see Jack looked scared (maybe as he sees the kids), and then he puts on a brave face as he turns and faces Pitch.
My thought? Jack was going to give himself up to Pitch for whatever it may be worth. Jack’s the only Guardian with powers at this point, so he’s really maybe the only one worth something to Pitch. And even though it’s a long shot, Jack knows Pitch wanted to join forces.
Jack’s trying to strike a deal with himself as the bartering chip, most likely for his death.
He’s willing to do everything it takes, give up his life and his freedom (the only thing he had for 300 years) to have some sort of chance at protecting these kids, even though Pitch isn’t really all that great with keeping deals.
I think this is another point where Jack matured greatly. /shrug