That's one of the hardest things you have to do in your life. It's challenging to get over someone you have never dated, even if it seems like an easy job to some. But, please remember, you have two choices: either stay right where you are and continue destroying yourself over something you never had and can never have or try to get up, help yourself and move on. The later, the harder choice but a better one.
Firstly, I would say, get your mind and heart on the same page, that is, you have to move on. The phase of waiting for them is over. Now it's about time you let things go.
Secondly, get on the preparation. Plan a schedule to keep yourself busy. Include all the hobbies, activities, things you have wanted to try, no matter it's cooking, baking, reading, drawing anything. Try new things and experiences. Thirdly, work on it. Follow your schedule, keep yourself busy but don't overwork yourself, your body needs rest. Try new activities, which caught your interest in the past but you never got the chance to try it. Go for walks, dress up, try to enjoy every little things that happen in your life. Do things for yourself. Try to hang out in new friend circles, talk to new people, go on dates. Eventually, you will realise, the world is vast. Many more interesting things and people lie beyond your beloved.
However, never try to deny your feelings. That makes them want to express themselves more. Accept them, acknowledge them and let them go. The more you try to bury them, the more you find it hard to let them go. It's alright to feel whatever you are feeling. Don't name them if you aren't comfortable. They aren't supposed to be named, either. Feelings are only there to be felt.
Another point I would like to talk about is, at some point, you might feel like your wall is breaking, you might crave for them, you might miss them, want them. It's okay. Don't be harsh on yourself for feeling so. But stick to your plan in any case.
It will take time but it will happen. You will get over them once you decide to.