OkCupid
Questions & Answers

The best way to retrieve deleted messages from OKCupid is to contact the company help line as a kind of authority (INTERPOL, Police...), else, deletion of messages from the personal user members area is dead and gone.

Unless they have everything backed up, you're out of luck.

I think the only way would be to contact OKCupid staff and see if they can help. When you delete, you delete.