"I don't know what I wanted. I just - knew that I had to keep working," Gale replied, hands loosely linked, elbows on his knees. These beds were small and he was not - and he was half worried that he'd sink Gretel's mattress, and then he'd feel bad. "Keep fighting. I just kind of dove into the system that created Snow, dismantling it, making sure it never happened again. His supporters are still out there, pockets of pro-Snow groups. I don't think you should have had to deal with that. You already dealt with enough."
Katniss had been their Mockingjay, she'd been used and abused and not to mention what happened to Peeta - Gale couldn't blame them if they didn't have any fight left in them. It wasn't up to them, it was up to the other rebels. Katniss and Peeta had long earned a restful life, or at least a shot at one.
Admittedly, he didn't know how to shut off the part of his brain that was jolted into action when the rebellion began. He didn't think he ever would - because that meant becoming complacent, leaving room for the whole thing to start anew and he would never let that happen. The idea of their blood, sweat, and sacrifice being for nothing was abhorrent. "I still missed you though." If that meant anything.