Fire
In the summer of 1978, James Potter has a bit of an epiphany.
He realizes that the only sure-fire way to erase depressing, angry, or otherwise stressful thoughts of the war from his mind is to make love to Lily.
On a particularly humid night in July, they really, really need to forget.
As she pushes him down onto the bed and climbs on top of him, every nightmare vanishes from his consciousness and all he can focus on is the fire pulsing through his veins and the way she tangles her hands in his hair when he kisses her neck. His lips trail from her neck to her ear, and he delights in the girlish giggle this elicits from her. Then he finds his way inside of her and her giggle becomes a moan, and he wonders how he could ever have gotten this lucky. She is everything he needs in his life, and he loves her more than he can ever say. He knows she understands. But he tries anyway. He kisses her urgently, hoping that his kiss will say what he can't say out loud.
It's always like this after a particularly bad run-in with the Death Eaters. They make love frantically, intensely, passionately. They lose themselves in each other. And it helps them forget. Marlene McKinnon, dead and mangled on the ground. Molly Weasley, wailing at her brothers' funerals. He forgets it all as Lily moans his name and he silences her mouth with his. The feel of her hands on his skin and her lips trailing down his body seem like the only good left in the world after a day like today.
Afterward, she sleeps on his chest. He knows she can't sleep soundly unless he is there, his arms wrapped protectively around her. But he still can't sleep. He knows he will never be able to protect her from everything, and that kills him. He shifts a little, and she wakes. They make love again, because it's the only way to keep the nightmares away.
He wakes up the next morning much too early, and he feels guilty. He feels guilty that they are carrying on blissfully, locked in their bedroom, closed off from the world. He feels guilty that his friends are probably drowning their sorrows somewhere else, without him. But he can't help it. The feel of Lily's body connecting with his reminds him what he is fighting for. He is fighting for her. He is fighting for everyone like her. He is fighting for a long and happy life with Lily by his side.
He is fighting for a day when they won't need to forget.