Not contacting someone, initially, can be really hard.
I went no contact with someone once (amicably), I just sent an email and said, I don't think we should talk to each other for a while (we had already broken up but were in regular, daily, contact).
He didn't reply and that's fine.
Then it was a struggle. So I would break it down in to increments, to days, when I was feeling stronger (I won't contact him today, but I can tomorrow if I want to) to a few hours on days when I might feel sad or wanted to speak to him (I won't call/text for the next hour then see how I feel - or 10 minutes etc). I found in every case, after the hour or day went by, I was usually feeling stronger and didn't feel the need for contact.
We all have days when we are feeling happier or stronger or more confident than others and those days are a bit easier, but it's those not so happy days where you can struggle. I knew that nothing - absolutely nothing good would come from contacting him, however, I still gave myself that option if in a day (or hour or half an hour) I still wanted to.
That's what I mean by increments. Break it down in to time periods that are manageable. It's a plan and if you follow it you will probably succeed. It's not perfect, but it gives us time to stop and think about what we are doing and hopefully resist making contact (because sometimes you know, it's just not worth it).
Another thing to do is keep yourself busy. When you are sitting ruminating about the "good times" and get the urge to make contact - get up and go, right away. Go to the store, walk down the block, put on a movie, make yourself a treat for later or start making chili, call your friend, browse for a new book online or a new shirt, play a game that takes concentration. If you are at work, grab coffee and have a 5 minute conversation with a workmate or give yourself a pep talk (in your head lol).
I never spoke to him again and I don't care! I really don't, time and distance gives us clarity, it will get easier as you go along and when you are out of this painful period you will probably wonder why you bothered with him at all, there is nothing good there. Your contact with him adds nothing good to your life does it?