Few relationship questions are as polarising as whether or not you should remain friends with an ex.
For some, it is easy to salvage the good and forget the bad but for every one of those, there exists another who would rather move on and cut all ties entirely.
In my personal opinion both sides of the argument are valid dependent on the nature of the relationship, the circumstances under which it ended and whether or not it poses a threat to current and future relationships.
I think for a platonic and functional friendship to flourish between exes, the very foundation of their union should have been based on a friendship. Short of that, there really should be no reason to remain friends with an ex.
By saying this, I do not mean do not remain pleasant and cordial when you bump into them but there is no need to remain in contact if you did not have a friendship to begin with or something tying you to each other for example children or a tight knit circle of mutual friends.
To move forward in a friendship with an ex, one should ask themselves the following questions. Is it worth it? How does this person make me feel? Am I over any lingering feelings I may have had for them in the past? Does this affect my current relationship in a negative way? Or if you are single, does it have the potential to blur any lines and hinder me from moving on to another relationship?
Only after answering these questions fully and assessing how this might affect your life should you proceed with what course of action to take. Personally, I feel like it is complex ground to navigate.
In the case that you have moved on with your life, it may come off as disrespectful to your current partner in the court of public opinion or even to the said partner if they are not very secure in themselves and trusting of you.
Exes should always tread lightly seeking or maintaining friendships when one or both of them have moved on to other partners. You need to check whether they are okay with it. Are they comfortable or does it threaten the basis or foundation of the current relationship?
If the relationship was toxic, embroiled in abuse and things ended on really bad terms, then perhaps forego a friendship. Forgive if you must, but ensure no ties remain because leaving lines of communication in such a situation open only leads to manipulation. Manipulation that would see you crawl back into old habits and maybe old circumstances.
There can be easy ways around such friendships too. For example, in the case that you were friends first and gave the romantic side a try but it did not work out but are better off as friends, I feel like that is non-threatening enough for you to continue.
You are both fully aware that love in that regard was not for you and can now communicate that to each other and your partners and let your friendship flourish.
There is not a definite answer on whether or not to stay friends with an ex. It can be very circumstantial, subjective and situations are always going to vary.
It is up to you, the individual, to assess the state of your life, how a friendship of that nature would fit in, whether it is developmental or worth your time to pursue. If all things align in your favour, then proceed. Should they fall short, then that ex is not someone you need as a friend.