- In Magic, "you" usually refers to the current controller of a permanent, spell, or ability.
- Changing control of a creature does not change control of the Auras or Equipment attached to it.
Thus, when the Ordeal triggers, Player 1 (the player who cast the Aura) still controls it even though Player 2 (the player who cast Portent of Betrayal) now controls the creature it enchants.
Note that you could even enchant an opponent's creature from the get go (since it says "Enchant creature," not "Enchant creature you control"). Some Auras are straight-up designed to be used this way (e.g. Pacifism), but sometimes even the ones that aren't can be used for clever tricks.
109.5. The words “you” and “your” on an object refer to the object’s controller, its would-be controller (if a player is attempting to play, cast, or activate it), or its owner (if it has no controller). For a static ability, this is the current controller of the object it’s on. For an activated ability, this is the player who activated the ability. For a triggered ability, this is the controller of the object when the ability triggered, unless it’s a delayed triggered ability. To determine the controller of a delayed triggered ability, see rules 603.7d–f.