Some nights, Gilgamesh dreams about Enkidu.
Not most nights. Most nights, he's awake, and when he does sleep, his dreams are an endless expanse of nothing. That, or he dreams of other wars, other possibilities, other conquests. Striking down other Servants, Servants he could only name by their Noble Phantasms. He didn't remember them when he awoke. He only remembers that he dreamed, and he didn't care what he dreamed. If he did not remember, it was not important.
But, some nights - once, twice a week - maybe once a month, if he's lucky - he dreams of Enkidu. Sometimes, they're "good" dreams. He dreams of the fight he had had with Enkidu when they had first met - he dreams of unloading the Gate of Babylon for the first time, of being beaten into the ground by a clod of mud, of lifting Ea into the air, and of laughing and laughing with his newfound friend. Or of fighting any number of the foes they had conquered together, or just sitting with them, smiling, talking, laughing. He wakes up from those dreams and he can't sleep again. He wanders up and down the aisle of Kotomine's church and curses the gods before stomping out into the night looking for something, someone to vent on. But those are the "good" dreams.
The nightmares are far worse, and far more common.
He dreams of holding Enkidu in his arms while they fell to pieces. He dreams of Enkidu's last words, words he can't remember exactly when he wakes up, but words he hears in things random, meaningless people say, words that make bile rise in his throat. He dreams of the water washing the mud away, he dreams of screaming and sobbing as he dug into the mud and tried to bring Enkidu back. When he wakes up from those dreams, he does not cry. He just lies in his bed and stares at the ceiling and tries to breathe. But he can't. It feels like there's a weight on his chest, and he can't move. He doesn't want to move. He just wants to rot.
Eventually, he falls asleep again, and his dreams go back to blankness, and in the morning, he feels alive, again, and until the next dream, he is able to forget.
He is able to focus on the now. He is able to focus on his plans, with Kotomine. His plans for a new world; to give the world and its people meaning, again. The modern world has no treasures, and it has no heroes. But his world would. Once he was king, everything would return to how it was. Of course, Enkidu would never return - no matter how badly Gilgamesh wishes, no matter how hard he hopes. So, he ignores it. He ignores the empty feeling in his stomach and runs his hand over the hilt of Excalibur and grinds his teeth together. Three more years. Three more years, and everything would be his.
The grail, Saber, the world, and the future.
There was no time to dwell on the past, even if it'd haunt him until the day he died.