Almost everybody has something negative to say about their previous relationship(s).
You could hear statements like:
I wish I never met him/her!
You can burn in hell for all I care!
Watch me get better!
I am just doing fine without you!
Blah blah blah!
How about those times you were all over him/her?
He/she was your everything and every other good memories. So, suddenly, you guys fell out and made each others enemy list.
I really don't think it should be like this. That it didn't work out doesn't make you guys enemies automatically. A failed relationship is an opportunity for one to identify where mistakes were made, accepting them, correcting them and then move on with life.
You could still be friends with your Ex and of course with limits because I believe that there is more to life than relationship!
PS: The future is pregnant and one can't tell where help may come from!