Sometimes it can be hard to accept a new reality, when we'd become so comfortable in a previous one. A roadblock may form: "He was the one". That thought becomes the primary. It makes the future a muddle, and the present something you have to struggle to get on with. That's no way to live. There are a lot of good ways to get over a break up, that don't include surrounding yourself with a pain you don't deserve.
Understand that there are near 7 billion people in the world. This must sound cliche, and perhaps a bit insensitive; but there /are/ other fish in the sea. Not only that, but there are jellyfish and starfish, sharks and dolphins - all types of aquatic life. Meaning you don't have to accept this break up as the end of your love life. Just try to visualize yourself romantically happy again. Even if you don't believe it yet, slowly, it'll help you broaden your horizon.
Second, try to give yourself a break. It helps not to be surrounded by triggers that get you feeling negatively nostalgic, since hurtful memories are the last thing you need to be able to move on again. Don't go ripping through your photos and trashing old memoirs yet, but instead, surround yourself with symbols of a fresh start. That can mean doing something as simple as going shopping, starting some new innovative project, joining some new fandom or club, even discovering a new part of town during a slow-paced car ride. This can help you start that new chapter in your life feeling fresh.
It's okay to be upset, and to struggle to move on. That feeling of sorrow gloominess is an essential part of moving on, as long as you don't let it take you over. A good way to make sure you're kept safe, is to surround yourself with loved ones; friends, family, pets even? Remind yourself that you're not alone in this.
Motivation is a big push forward. Sometimes relating with people who've been in your shoes, or have been in your shoes, helps you envision a successful moving-on. That's what makes this website - and the entire internet really - so great. Don't hesitate to check out forums like the one we have here on 7 cups, and browse the internet for stories like yours.
Your experiences with this relationship will make you stronger, and will help your love life in the future prosper. I wish you the best of luck.