Depends on whether your ex is actually making an effort to keep up a conversation with you, and it sounds like they are. My ex said she just wanted to be friends after 3 weeks of dating, which I reluctantly accepted. She immediately started ignoring my messages, disappeared completely and didn't do anything to show that she wanted to be friends. I got fed up of making an effort so I deleted her number and never contacted the ***** again. On the other hand, it sounds quite amicable between you two and as you said it was a mutual break-up, it might not be so bad for you. Just stay on the side of caution and don't let the conversation get too deep. How long has it been since you separated?