(I'm sorry for my bad english)
Everything in Lordran is just an illusion of Gwyndolin, come on:
In childhood Gwyndolin lost his parents in a horse accident, and was traumatized by it and then forbade horses in Lordran, so we do not see any horse in dark souls. Already in his teens he started dating a guy who was arrested for riding and who was this guy? Chosen Undead. But there was one thing, Chosen thought she was a woman (yes he is a virgin). After seeing his boyfriend arrested and losing his parents, Gwyndolin went into depression and isolated himself in an imaginary world that, because of his magic, turned into an illusion in Lordran. Chosen's mission is to kill Gwyn's illusion to end his girlfriend's fantasy once and for all. The two possible endings are metaphors for when Chosen discovers his girlfriend's sexuality (abyssal snakes are penis), if you choose to rekindle the flame you break up with Gwyndolin, if you choose to become the new lord you become gay.
Who is real in Lordran:
Oscar: Chosen's best friend and who paid his bail.
Lautrec: A badboy who loves riding horses and Anastacia, his gang likes to hit cool guys.
Solaire: The real nice guy, loves marijuana, lsd, estus and the sun.
Chosen: A guy who drank too much and ended up riding.
Gwyndolin: Waifu
Sif: The patrol dog that kills who rides a horse
Dark Souls doesn't have a plot, it's literally random shit they made up as they went along in hopes that easily manipulated idiots would think it was deep because it didn't make sense. Stop wasting your life on this shit.