Why do I use another number to send a message to my ex-boyfriend so that he can guess who I am?

If your ex-boyfriend can guess your identity, there may be several possible reasons:

1. He may know your mobile phone number. He may know that this number is yours before, or he can recognize that this number is yours in some way.

He may notice your language or content. Your words, tone, topic, etc. It may reveal your identity and let him guess your information.

He may have done a background check. He may have found out your other contact information in some way, such as your name, address, social media account, etc. To guess your identity.

In either case, the fact that he can guess your identity does not necessarily mean that he is following you or has bad motives. He may just know some information about you, or your information has been leaked in an open channel. Anyway, if you don't want him to guess your identity, you can try to change the number you use or change the way you communicate with him.