Yes. It is doable.
You can remain friends with a person if you don’t secretly expect and hunt for the old relationship.
You’re going to have to admit that the past is in the past and the future will have something new for you. Let go of the past, remember it with a good word and be open for anything for the good future.
One other thing when it comes to having been in love – it might help if you try to understand how this relationship with that person was validating your own ego. Often we “want someone who wants to be” with us only in order to get some validation on our own worth – are we pretty, are we smart, are we important, are we valuable – we all want to feel this way – and even though a person with a healthy self-esteem will feel pretty, smart, important and valuable no matter if they are in a relationship or not – we as fragile human being tend to be a bit comfy and seek confirmation from other people in order to feel right. It’s a good science, worth looking into if you feel like you can’t get over it.
Take care o/