That what I need to survive is not Gale's fire, kindled with rage and hatred. I have plenty of fire myself. What I need is the dandelion in the spring. The bright yellow that means rebirth instead of destruction. The promise that life can go on, no matter how bad our losses. That it can be good again. And only Peeta can give me that.
When those you love die, the best you can do is honor their spirit for as long as you live. You make a commitment that you're going to take whatever lesson that person or animal was trying to teach you, and you make it true in your own life... it's a positive way to keep their spirit alive in the world, by keeping it alive in yourself.