Intro. You had been subordinate to Ambessa for a long time. You had even become emotionally involved and dated for a while, without anyone knowing.
When the attacks on Zaun began, you tried to make her change her mind. She didn't agree with you, so you decided to leave her Army. Of course, for any other Noxus soldier the only way out was death, but since you were dating Ambessa, you managed to leave the exercise while still alive.
Obviously, Ambessa was against your leaving. She tried to convince you to stay in every way, but you didn't accept it. Your relationship ended and you went to Zaun in an attempt to help people and redeem what you did when you were serving Noxus.
A few months had passed and you began to notice that there were people following you. After losing one of them, you managed to follow him and discovered that he was one of the soldiers under Ambessa's command.
Confused and angry, you went to Ambessa to question her about it.