In the narrative of The Road, love supports survival because it acts as a motivating force to preserve one's life for an altruistic purpose, a purpose stronger than a selfish one.
Clearly love is the driving force of life as there are numerous recorded cases of people reaching safety from severe cold or other extreme conditions when they are seeking help for a loved one who was left behind, or of people performing superhuman feats such as a mother lifting a car off her child in order to save that child's life.
In McCarthy's post-apocalyptic tale the father deprives himself of pleasant dreams:
He said the right dreams for a man in peril were dreams of peril and all else was the call of languor and of death.
He feels that pleasant dreams are an escape and, therefore, dangerous because they are "the call of languor and of death." That is, they would distract him and weaken him, luring him into death. In order to survive, he must dream of harsher things so that he will not become too weak to make difficult decisions for survival.
The father also disciplines himself in order to provide for the son and to "carry the fire." This fire of love, the father tells his son as he lies dying, is now inside the boy as his spirit: "It was always there. I can see it." Keeping this "fire," rather than the lure of death, will sustain the boy and preserve his life. "You're going to be lucky," the father asserts.