Start by editing his contact in your phone (if you have a smart phone - I do not know if regular phones have this capability) and put his calls through to VM so that you do not hear beeps when he calls. If he leaves a VM, listen to it but do not respond. Think about whether you need to respond first.

If you use GMAIL, auto archive his emails on arrival and look at them when you have time. If you use Outlook, create a folder for his emails and a rule to route his emails into the folder. I do not know how to achieve the same result in other email clients, but this is a technical issue that can be resolved if you ask around or tinker with the settings. Do not bother responding instantaneously.

Do not respond to texts unless he says that he is experiencing symptoms of a heart attack, and even then, just tell him to call 911.

That should create some distance, and in the meantime, use some therapy perhaps to help you distance yourself even further.

Make sure you perform well at work and all of this inner battle with yourself does not spill over at work.