In a previous post, I analyzed what it means to be friends with your ex.
Although 90% has a crush on you, there is also that 10% who really pretends to want you as his girlfriend, which although it seems difficult and strange, is not impossible.
To do so, a long period of time must have passed and, most importantly, you must have overcome it.
If I had to stay friends with an ex, it would definitely be someone we didn't spend much time with and who didn't hurt me or lie to me.
It's not possible to become a best friend overnight, nor are you obligated to sit and listen to his current one, but neither is he obligated to listen to your crying about every next one -unless you're large-
The truth is that I have also kept in touch with my ex, but we are not stick-it-together, but we say the formal things and whenever necessary.
Simply for this to happen, you have to clarify within yourself what you want and then proceed amicably with him.
Besides, exes are like bombs ready to explode, because with the slightest thing, you either break everything or the deeply well-hidden feelings come back to the surface.