Is it permissible to talk to an imaginary person as if they were a spouse, and to imagine married life with them?

These fantasies are a type of daydreaming, and the default is that one is not held accountable for them unless they lead to a statement or an action.

We advise you on two matters: 1. Occupy your time with beneficial knowledge, righteous deeds, and cooperating with righteous women; for time is precious. 2. Seek a means to get married by supplicating frequently and seeking help from trustworthy relatives and friends, for it is permissible for a woman, according to Islamic law, to seek a righteous husband.