Katniss didn't settle for Peeta, she didn't say well this is as good as it gets...no she actively chose Peeta every single time. She knew him intimately when she described him with swoon-worthy words:
You're a painter. You're a baker. You like to sleep with the windows open. You never take sugar in your tea. And you always double-knot your shoelaces.
She always thought of him...chose him:
When he was reaped she expressed immediate remorse "Oh no not him, not the boy with the bread."
When he was reaped in The Hunger Games: "To this day, I can never shake the connection between this boy, Peeta Mellark, and the bread that gave me hope, and the dandelion that reminded me that I was not doomed."
In the Arena, the Hunger Games: “The idea of actually losing Peeta hit me again and I realized how much I don’t want him to die. And it’s not about the sponsors. And it’s not about what will happen back home. And it’s not just that I don’t want to be alone. It’s him. I do not want to lose the boy with the bread.”
To Haymitch in Catching Fire: ″‘Like you said, it’s going to be bad no matter how you slice it. And whatever Peeta wants, it’s his turn to be saved. We both owe him that.’ My voice takes on a pleading tone. ‘Besides, the Capitol hates me so much, I’m as good as dead now. He still might have a chance.‘” (Katniss was ready to die for him and is begging Haymitch to die for him too)
In Catching Fire the Arena: I realize only one person will be damaged beyond repair if Peeta dies. Me. "I do", I say. "I need you."
In District 13 in Mockingjay: I drink in his wholeness, the soundness of his body and mind. It runs through me like the morphling they give me in the hospital, dulling the pain of the last weeks.
In District 13 in Mockingjay, she is deeply depressed without him. She is suffering from PTSD and doesn't have her support system there. She misses Peeta. Katniss pines for him - keeps the pearl he gave her nearby...
"Sometimes when I’m alone, I take the pearl from where it lives in my pocket and try to remember the boy with the bread, the strong arms that warded off nightmares on the train, the kisses in the arena."
"My mockingjay pin now lives with Cinna’s outfit, but there’s the gold locket and the silver parachute with the spile and Peeta’s pearl. I knot the pearl into the corner of the parachute, bury it deep in the recesses of the bag, as if it’s Peeta’s life and no one can take it away as long as I guard it."
By the end of the book, after watching her sister die, and having shot Coin - Katniss loses it...and she becomes almost catatonic. Katniss blocks out everything when she comes back to District Twelve in Mockingjay:
"I haven’t left the house. I haven’t even left the kitchen except to go to the small bathroom a few steps off of it. I’m in the same clothes I left the Capitol in."
She cares for nothing and is forced to eat it's only when Peeta comes back that she becomes aware of her appearance and it's when she literally begins to live:
"When I see him, I pull up short. His face is flushed from digging up the ground under the windows. In a wheelbarrow are five scraggly bushes. “You’re back,” I say. “Dr. Aurelius wouldn’t let me leave the Capitol until yesterday,” Peeta says. “By the way, he said to tell you he can’t keep pretending he’s treating you forever. You have to pick up the phone.” He looks well. Thin and covered with burn scars like me, but his eyes have lost that clouded, tortured look. He’s frowning slightly, though, as he takes me in. I make a halfhearted effort to push my hair out of my eyes and realize it’s matted into clumps." ...-... "Back upstairs, I throw open the bedroom windows to clear out the rest of Snow’s stench. But it still lingers, on my clothes and in my pores. I strip, and flakes of skin the size of playing cards cling to the garments. Avoiding the mirror, I step into the shower and scrub the roses from my hair, my body, my mouth. Bright pink and tingling, I find something clean to wear. It takes half an hour to comb out my hair. Greasy Sae unlocks the front door. While she makes breakfast, I feed the clothes I had shed to the fire. At her suggestion, I pare off my nails with a knife."
Katniss chose to be with Peeta, just like she chose to live when he came back...
