What is the ruling regarding my living in an apartment by myself with a man who is not a mahram to me, while my room door is closed upon me, and what should I do to find a solution to this living arrangement?

It is not permissible for a woman to live alone with a man who is a stranger to her in the same apartment, even if each of them is in a separate room. This is because it constitutes an unlawful seclusion (khalwa), and the Prophet, peace and blessings be upon him, forbade seclusion with a non-mahram woman. Furthermore, scholars have stipulated that for cohabitation between non-mahrams to be permissible, shared facilities such as the kitchen, bathroom, and hallway must not be common between them. Accordingly, the woman must leave that apartment immediately.