ANSWER:
This was bound to happen, as it is common in such ‘relationships’.
What is the extent to which you are willing to let him blackmail you?
He will soon have you physically doing his bidding, by such blackmails.
You do not need to give any explanations to him whatsoever, simply cut off all communication and repent to Allah for the being in such a relationship in the first place.
If he forwards the videos or pictures, You can simply claim all the ‘evidence’ is photoshopped or fake. Many women who feared being blackmailed like this ended up turning as prostitutes and giving themselves to his friends so that they won’t be exposed. They were all eventually exposed with their porn movies all over the internet! You must not give in to his threats no matter what happens as this is the will of Allah and you have to face the consequences of your own choices and be patient.