Gale never really went to District 2. He died on his hovercraft back to District 12. They could never break it to her. Even the other victors knew. But one day, 25 years after the 2nd rebellion, She found something that made it all clear to her.

Katniss's Pov
Even after having children and having a loving husband who experienced the same thing as me, the forest is the only place I can be me. I still have a bow, Not the same one as the one my father made me, that one rotted away a couple of years ago.
I still hunt, even though most of the district isn't as poor as it was all them years ago, I go to the lake my father taught me to swim at. It occurred that my father saved my life in the second Quarter Quell if I didn't know how to swim how would I have got to the Cornucopia? Would Gloss of killed me? Or Brutus for me declining his offer for joining the Careers? It saddens me that they're all dead now. The people, most feared 25 years ago, are now all dead but two.
Just as i notice something in the trees. It looks like the hovercraft that got me out of the arena. And the thing that killed Prim. Why her? Why couldn't it be me? She had so much to live for. She could of been a Doctor. Gale, Even though I partly Blame him for her death, I miss him, why can't he come home? He has a mother and Siblings who miss him so much. Blaming Gale for killing Prim is like Blaming the person who made the gun that killed a man. I keep telling myself this but I can't get it out of my head it was him who killed her.
I have nightmares about Gale driving a sword through Prim's Heart then Peeta's then mine.
I walk closer to the Hovercraft and see a deer. I aim at the deer until I see Skeletons. I let out the highest Squeal that I have ever heard. Did I just made that sound? I walk over to the Skeletons but I trip over a piece of Metal and land just under a badge that read. "Officer Hawthorn."
It can't be. He's not dead. No. But.. Then it kicks in. They knew? Why did they Lie?

Peeta's Pov:
Katniss comes Barging in the door and Pounces at me. I just about turn it into a hug before it gets out of hand.
"Why didn't you tell me?" She says.
"Tell you what?"
"About Gale"
I sigh. "It was for your own good, He wouldn't of wanted you to know. There's a note in the box under our bed. Bring it down and i'll read it to you."
She storms out the room up the stairs.

Katniss's Pov:
I bring down the note and hand it to Peeta, Whom i am still mad at,
He Clears his through and begins
"Dear Peeta,
I have limited Time. We'll crash any second.
Keep her in good hands. Please?
I never hated you. I was jealous of you. It would be a lot easier If you weren't so nice. But I know why she loves you. Don't take this offensively but you killed 1 person in both of your hunger games. (Well I don't think the redhead should count seeing as you didn't expect her to eat the berries)
Tell my family, Tell whoever, Just don't tell Katniss. Please?
I couldn't bare her knowing that I died this way. Helping the win the rebellion then dying in a hovercraft.
I know you can make up a story about where I went.
Prim was like a sister to me. I would never kill her.
If she does find out. Tell her I l-"
The Note ends there.
"Is there more?" I ask.
"He wrote this with 30 second of his life left. I think he didn't get to finish it. I think he meant he loves you"
I fall down and sob until I have no tears left. He's dead. Never coming back. I wish i could tell him. That I love him too.