Wechat is not added, and I will reply occasionally when I send a message.

Wechat doesn't add friends, and occasionally returns messages. It may be that the other party is maintaining his social circle and interpersonal relationship, but at the same time he doesn't want to expose his private information to strangers or increase his social burden. Or, it may be that the other person has a good impression on you or at least is loyal to the past friendship, because you have the same understanding or experience. However, if the other person always doesn't add you as a friend, he doesn't reply a lot of messages.