Relationships, friendships, situation-ships...any "ships" really are a trial and error scenario as you try to figure out what works for you while gaining an understanding of both yourself and others. So perhaps you've done the song and dance of dating, you've entered a loving relationship and it lasted a significant time, but then it came to an end for one reason or another. Mutual agreement or by Maury like drama, it came to an end and you've come to terms with it. There might be a time where you blocked them on social media or just avoided them at all costs to prevent that heartache of not being in their lives anymore. One day, the sun will shine, you will see the silver lining from this breakup, and everything will be right with the world. Then, just when you think it's safe, you'll receive that text from your ex. The "Hey, how are you?" casual and yet still jarring message. Now you are faced with the simple question of, "Can I be friends with my ex?"
The answer is no.
Well, that would be inherently biased, right? So let's upgrade that "no" to a "not really."
In reality, I find it possible that any two people could be friends and former lovers even more so because of their intimate understanding of each other. But that understanding could also, in theory, cause a crossing of boundaries. Friendships take work and the de-escalation from intimacy to friends takes even more work. The same jokes you used to tell and the memories you once shared are now things of the past and have to remain there. Why? Because if you carry them on, you will not be able to move on.
The other key thing that leads me to land more on the "no" side of this argument is what happens when you do meet someone else. Friendships are supposed to remain intact even in a relationship. There is no doubt that your new beau will not want an ex deep in the picture. So you will end up restructuring the friendship to suit your relationship. This can play out positively with no hard feelings, which is a quiet yet rare interaction. On the other hand, it could play out negatively in which your ex is possibly going to push back on these new boundaries and cause friction in your own relationship.
However, there is the possibility that you avoid both sticky situations and really remain friends. It is possible that you two act as if the relationship never happened and appreciate the connection you two still have. But what does that actually mean? Does that mean you wasted your time together because you found out you were better off friends and by extension, never really loved each other as lovers do? Or are you content with the self-discovery as it is because you gained a better understanding of what you want in a partner?
This all leads us back to the "not really" point of view because it's all very personal. It's all about what you consider to be a win or a loss and how silver that silver lining was in the break-up. If you kind of find a way to concurrently love and appreciate your ex without compromising your future, then perhaps being friends with an ex is a no brainer. But if you find that you can't be happy for them without being happy yourself first, then perhaps it's best to leave them in your past.