Sending messages to ex-girlfriends, sometimes returning, sometimes not returning.

It's normal, it may be that the text message was delayed, but in many cases it may be that you did what you were doing before you went back. Maybe what you're thinking now is, send a text message, and she will definitely reply, or even wait for a long time. If she doesn't answer you, she will still feel very uncomfortable. This is normal, but you have to overcome this kind of heart.