I saw your other thread, and you're doing really well so far. It's one of the hardest things in the world just to take that first step.
PP are right, you must not only BLOCK him on everything and DELETE his phone number, but you absolutely must also DELETE HIS MESSAGES. Purge every line of access you have to him on your end, whether it's social media, stored texts, facebook conversations, emails - ALL of it. Now. Right now. And don't go undoing any of it!
He is like a drug, and anyone who is in recovery or knows somebody in recovery would tell you the most dangerous thing to you right now is having access to this drug... yet here you have it to hand at all times! You'll never be able to quit if it's right there, easily accessible by just lifting a finger.
To continue the drug analogy, throwing away that packet of cigarettes or bottle of whiskey is one of the hardest first steps for an addict to take, but it's easily the most necessary - right after admitting there is a problem (which you've done)! You can't drop a habit if it's staring you dead in the face; it's far too easy to convince yourself that you can have one last hurrah, that you deserve to reward yourself for a day without, that it's just this once.
Seeing his name in your phone is overwhelming temptation. Knowing that memories of the good times are right there is even worse. Delete the access that you have to him! Get him out of arm's reach first. That's in your control.
Then WRITE! When you're feeling lonely for him or tempted to daydream about better days, sit down and write - in a physical journal, a notes page on your phone, a draft document on your computer, this very thread, whatever.
Write down the reasons you left him, the things he did that made your life hell. Expand on those and go into detail. Remember the things he did, the way those things made you feel, and the emotions you had at the time. Feel those things again, and put those feelings into words. Once you start, even if you feel a bit of writer's block, I suspect the past will come flowing out.
Then when you start to pine for him again, go and read those thoughts back. Add to them. Dredge up the anger that enabled you to leave in the first place.
Also write about the good things you have now, the freedom, the things you're able to do that you couldn't before, the things you want to do in the future which you wouldn't have been able to do with him. Make plans and enjoy your freedom.
If you haven't yet, read up on the script and abuser tactics. They are incredibly predictable, and it may surprise you. He will say extremely predictable things to try changing your mind about leaving him (because if anybody's leaving anybody, it's him as he must be in control, whether he even knows it or not). He'll tell you he's going to change and may even detail how, he'll beg for another chance and even cry, he'll threaten suicide, he'll threaten you, and on and on.
Prepare yourself for those attacks, in the event that he does get in contact with you. Steel yourself against them, see them for what they are, and don't let them get to you. Once you know what's coming, you'll realise it's a bloody joke and it will affect you less.
You can do this. And we're here to help, so use us! Too many of us have been through this and seen the other side, and we can help you through it.