Most Helpful Guy
in my opinion a relationship with an ex has two outcomes, friends with benefits or start dating again1
Most Helpful Girl
If it was a mutual breakup and you have no leftover feelings maintaining a friendship will be a lot easier. If there is some leftover feelings, then there will be some resentment and he might just want to try to win you back.
I personally tried this with my past relationship, where I was the one to break up and it just ended up with him pushing my boundaries far more than I was comfortable with because he still liked me. It ended up going much further into creeper-mode than it ever did in the relationship, even though I had stated clearly I was not interested.
That situation may well have been person dependent though. If it's someone who can maintain healthy emotional distance as well, you might be fine.2