That rule is an interesting one. Is it a good idea to make such rules? https://twitter.com/mpumi_phillips/status/1247979631174615044

I think you should just set boundaries for yourself like - I will not date someone who talks to their ex. Agreements make things confusing, whereas boundaries make the actions to take when someone is breaching them more obvious.

Think of a relationship and everything that comes with it as something you are inviting into your space and not "our space."
That way it's clearer to you what you have control over and what you want or do not want in your space.