I once slept with my cousin brother and i regretted it, now he’s coming back for more..

Hi guys :I know it sounds stupid by doing this but believe me i will leave to regret my actions, i remember making love to my i cousin brother in my house under the influence of alcohol, after the incident, we promised never to repeat it again and to seal the idea of committing that abomination, Weeks after the devilish incident, he has been trying to put me to bed severally, what should i do guys because he threatens to tell everyone if i refuse his last offer this time…..