I'm having good relations with all of my ex boyfriends. But I can't call them my friends.
For example, for me, as a woman, is unpleasant if my boyfriend or husband is friends with his ex girlfriends.
I mean those "friendship" relations, when you share the most personal and call every time you need some advice. Guess I would not accept that if my partner had such relations, so don't do the same from my side.
My best friend is my current partner, as long as I want to grow our feelings and develop our relations.