I think it's possible to be friends with your ex. I'm not sure if this is something that is good though.
What do you imagine it would look like if you 2 were just friends? Are you able to look at him and not think about romance or love? Is he the kind of friend you would like to have in your life?
I definitely don't think you should be friends now with the hopes to be more in the future. That's certainly going to cause pain in the long run.