was mistaken, were mistaken, was cheating on, were cheating on
Quand tu étais marié avec elle, tu la trompais souvent ?
When you were married to her, did you often cheat on her?
— L'Agent secret (2025)
Ils ont dit que je te trompais quand tu étais à l'armée.
They said I cheated on you while you were in the army.
— Nang Nak (1999)