Like when we get sober, it's a day at a time. This too can be a day at a time, until you are comfortable enough with reality without him (like the reality of being clean and sober) that forever seems like a pretty good thing and no longer has ear attached to it.
In the meantime I'd suggest blocking his number so that he cannot call or text you, or contact you via social media. Tell mutual friends that if they relay messages about him then you will not be able to speak to them for a while.
I think that people with addictive natures can easily get a bit addicted to unhealthy relationships. The drama. The excitement. The hope and false illusion of being The One. The one person that understands this person. The one person they turn to. The person they love and want SO much that it makes them behave like a madman. And like all addictions, this has a large risk attached and a heavy price to pay.
I hope that you will lan into your fears, see help if necessary (CoDa or AlAnon) and stick close to those who love you and can demonstrate this in healthy and positive ways.
Take care. BB