What is the ruling of Islamic law on a suitor selling an apartment he owns in order to live in his fiancée's apartment and share half of it, and what is the effect of that on his role as maintainer?

It is permissible for you to sell your apartment and live with your wife in her apartment, whether you share ownership of it or it remains solely her property. This does not negate your guardianship (qawamah) over her; for guardianship is established for the husband by Allah's preference for him, and it is not contingent solely on financial support. Abu Bakr ibn al-Arabi mentioned that guardianship belongs to the man due to his perfect intellect and discernment, his perfect religiosity and obedience, and his expenditure of wealth through dowry and maintenance.