Don't usually means don't, don't want to

Nian means miss, miss

The general meaning is don't think about it, don't forget it.

But I can’t guess the meaning after looking at this

Your girlfriend probably just thought of a good signature, and she feels quite literary.

If you insist that this is some kind of inner expectation or a true thought that is meaninglessly exposed

It can be understood as two meanings

Don’t go Miss someone and don’t forget someone

or

Someone don’t miss me but someone don’t forget me either.

It is still not recommended that you think too badly, just ignore these words.

The first is to be tolerant, and the second is not to destroy your relationship.