Perhaps I am confused, but why did you feel it necessary to tell her ex-roommate the news that you broke up? I am sure this is why your ex-gf is really upset. Because the only thought that makes sense to her is that you did it because you wanted to hit on her. And that you have been thinking about it for a long time. Why else would you call her?
If there is another reason, that is fine, and I am not saying you were necessarily wrong for calling her, but I just don't understand the why and your ex probably doesn't either.
As for getting over her, time is the only answer.
As for your friendship, if it is as strong as you say it is, with time she will allow herself to be friends with you again.
Good luck.
Brought to you by Dating With Devon!