How we cite our quotes:
Johanna grins, and I feel a slight but significant shift in our relationship. I don't know that we're actually friends, but possibly the word allies would be accurate. That's good. I'm going to need an ally. (17.21)
Sometimes a friend isn't as necessary as an ally, particularly in a time of war. Here, it seems like Johanna and Katniss are almost in between the two: somewhat allied, somewhat friendly. Either way, they're closer than they were before, and Katniss can finally feel less alone.
I don't know if it's the pods, or the fear, or watching Boggs die, but I feel the arena all around me. It's as if I've never left, really. Once again I'm battling not only for my own survival but for Peeta's as well. How satisfying, how entertaining it would be for Snow to have me kill him. To have Peeta's death on my conscience for whatever is left of my life. (21.14)
Throughout all the terrible things that Katniss and Peeta have endured, they've worked to protect each other. They've continually put their own lives at risk to save one another. Even now that Peeta's been hijacked it's no different. They've got too great a history together and been through too much together to desert each other now.
Why can't I just let him go? Slip him a pill, pull the trigger? Is it because I care too much about Peeta or too much about letting Snow win? Have I turned him into a piece in my private Games? (21.51)
Katniss can't define her feelings for Peeta, or rationally explain why she cannot "let him go." She just knows she can't. But the reasoning for why she can't is escaping her. We'd like to think it's because of her love for and long-standing friendship with Peeta, but here it also sounds it may be because he contributes to her plan for revenge.