Why can’t exes be friends? (Yes, apparently I do need it spelled out for me – apologies.)
Relationships are either platonic or romantic. Relationships with your friends are platonic. Relationships with your exes, even though you’ve broken-up with them, are still romantic. In other words, a formerly romantic relationship doesn’t change the fact that the relationship is still fundamentally romantic.
Of course, you can be friendly with your exes. Very friendly. You can have perfectly amicable relationships after you break-up, but you are not platonic friends. You are exes. That’s why there’s a special word for it.
That’s also why a friend-with-benefits doesn’t become an ex once you stop fucking them. Platonic relationships tend to stay platonic, and romantic relationships tend to stay romantic.
This may seem like a bit of a semantic game, but the distinction between platonic and romantic is important, and respecting it can prevent all kinds of negative bullshit from invading your relationships.