See What you should not do when your ex texts you:
1. Do not respond immediately: After breaking up and deciding to be friends, replying to their texts immediately proves that they are still important to you. Do not make him or her feel like you are always available.
2. Do not jump into a conversation: It is fine to be friends but you should not give them a shoulder to cry on when they are experiencing problems. Since you both broke up, be careful how you communicate with them.
3. Refuse to be affected: Do not forget why you both broke up. Move on.