The exhaustion you describe is real, and the constant suspicion would wear down anyone. What you are facing is not the peace God calls a husband and wife to. Scripture reminds us that God has called us to peace, not to endless warfare within marriage, and cursing and accusation do not come from that peace.
You cannot prove a locked door to someone who has already decided not to believe you. Scripture records that accusations without proof remain unfounded. So do not let false accusation define your conscience. You are not required to win every argument or defend yourself all night. You are required to be truthful, patient, and faithful before God.
That does not mean you must pretend this is normal. God's original design is a lifelong covenant of one man and one woman, but the same Scriptures acknowledge that marriage can bring trouble in the flesh and that no spouse can single-handedly guarantee the other's peace or repentance. You are called to peace, and you may need wise boundaries while you continue to pray for her. Your first and constant refuge is the Lord, the way Jesus withdrew alone to pray and be renewed.
Keep loving her as Christ loves the church, with truth and patience, but do not feed the fear by endlessly arguing with it. Let your consistent conduct answer what it can. Pray that God would quiet her mind, expose any lie she is believing, and give you grace to endure without becoming bitter.
Father, I bring this husband before you. You see the exhaustion, the accusations, and the strain in this marriage. Give him steady love, clear wisdom, and protection from despair. Guard his wife's mind and heart. Silence the fear and accusation that are tearing at her, and bring this home into your peace. In Jesus' name. Amen.