Our professor taught us about these two delusions and upon further thinking I feel that Eratomania may just be a sub-part of Grandiose disorder. If this is the case then why are these studied as separate Delusions??
In my search that includes generic books like Psychology by Robert A Baron and google I'vs found no resource that answers this question!
All I've found are definitions!
A person with grandiose delusional disorder has an over-inflated sense of worth, power, knowledge, or identity. The person might believe they have a great talent or has made an important discovery.
Someone with erotomanic delusional disorder believes that another person, often someone important or famous, is in love with them. The person might attempt to contact the object of the delusion, and stalking behavior is not uncommon.