Firstly the credit card companies will not deal with you regarding your partner's cards - he will have to phone them himself , because of the Data Protection Act.
He would be responsible, not you. He is obligated by the terms of his card accounts to keep his PIN number secret and his cards safe.
However, you have committed fraud. It is not for your partner to decide whether or not charges should be brought against you, that is a matter for the card companies. It is highly unlikely they will if your partner comes to an agreement to repay the monies and sticks to it.
It is up to you and your partner to come to an agreement as to how you should repay him.