It's okay to be friends with your ex-boyfriend/girlfriend, but you can never be friends immediately after the break-up or else the friendship will fail. To be someone's friend you must be able to support them and love them. Relationships almost never end on good terms, so how can you be truly supportive to the person that broke you? You can't.
You both need time to heal and love yourselves again without the emotional support that you both have been leaning on for so long."You can't fix yourself while holding on to the person that broke you." -r.h.sin. Remember that.
Also, please for the sake of all your friends, followers, and your self-dignity, keep your relationship off social media. I'm not saying don't post want you to want to post, but when your profile has turned into a hate blog for your ex, I think it's time quit. Not only does constantly posting negative things about your ex make you look bad, but it also makes the healing process go even slower and possibly ruin the chances of friendship again.
And if you truly believe that sending a text that is close to the length of 400 words to your ex explaining once again that you are completely over them will make them change their minds then go off, but know it most likely won't work. Then didn't care the first time, they won't care the seventh time.
So basically, be respectful and be kind to your ex. No matter how messed upshot they did was and no matter how badly that hurt you, realize that treating them terrible back solves nothing and only reflects badly on you. You can't change how people treat you, but you can choose how to react.