What if the ex-girlfriend doesn't return the message?

Explain that your ex-girlfriend doesn't want to do things too well, and replying to your message is only out of courtesy in communication. This is a courtesy, you should not think too much. After all, people don't want to contact you, so it's better not to send messages, because not disturbing others is also a kind of rest.

It is best to do self-reflection in love, so that you can find your mistakes well. Although we broke up, I hope you can understand everything you did before. Don't bother others again!