Since what you sent was only for him (i.e. it wasn't 'published', as it would have been if it had been on, say, Facebook) it can't be 'defamatory', so there's realistically nothing that he could sue you for anyway.
He could, of course, refer the matter to the police as it's a criminal offence to send malicious messages but, if was only a single text (rather than prolonged harassment), it's unlikely that they'd want to get involved. If they did, your solicitor could seek a court order requiring them to disclose any relevant texts they still retain.