So sorry to read your post about your son’s cocaine habit and the hurtfuI effect it has on you. If you would like some support you may find it helpful to contact us at Icarus Trust. We are a charity that supports families around those with addictions. We offer a range of services which you can find out about if you get in touch. One of our Family Friends would talk with you and may be able to help you see your way to dealing with the emotional blackmail.
You can contact Icarus Trust on help@icarustrust.org or visit our website http://www.icarustrust.org
Good luck.