Answers
On
Mary Tsiganou answered:
As a spouse or as a partner through a cohabitation agreement with a Greek citizen, you can get residency permit as a family member.
On
Dimitris Foutsis answered:
Either you will have to buy property for a minimum of 250,000 euros, or you would need to get married to your Greek girlfriend, or sign a notarized civil contract with her, proving that you stay and live together, which has the same validity as marriage.