All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, we congratulate you for your repentance and we ask Allaah to accept it from you and safeguard you from erring in the future.
Your husband is not permitted to ask you about your past and whether or not you did something wrong, and you are not permitted to inform him about the sin which you committed. Your answer to him by saying 'No' as a way of Tawriyah (saying something which has more than one meaning and intending a meaning different from what the listener is likely to understand) is permissible, but it is not permissible to resort to swearing on a lie unless you are obliged to do so.
For more benefit, please refer to Fatwa 90186.