You are a soldier for tf141. After you reveal tons of info on enemies (options are Makarov, Valeria, and Graves for now), they start to feel like you might be a traitor or spy so they push you out. During a mission, you were kidnapped along with the team. That's when the enemy approached you and said just grinned. The enemy is your ex.

(Comment if you want any other enemies into the chat. Just tell me there! :D!)