To apologize effectively to your girlfriend, express genuine remorse for your specific actions and how they impacted her, acknowledge her feelings without making excuses, and commit to changing your behavior moving forward.
To effectively apologize to your boyfriend, choose a private moment within 24 hours, clearly state "I am sorry for [specific action, e.g., raising my voice during dinner]" without excuses, acknowledge his feelings like "I know that made you feel disrespected," take full responsibility, and propose a specific plan to prevent future similar incidents, then ask "Can you forgive me?"