Had your partner gone through the justice system and been charged with manslaughter on grounds of diminished responsibility? What do you actually know about that process, the correctional facility where he was detained, the length of time and how he was treated/stigmatized whilst detained.
He cannot stop 'with the lies' because they are intrinsic to protecting his being from the horror of knowing that he was responsible for the death of his mother.
You are out of your depth @Rilke