"Do you have a girlfriend?"

[Stergi3]

The indefinite artcle is not used so much as in English. Sometimes ένας/μία/ένα is a pure arithmetic. Do not compare the phrases with the similar ones in English. Native speakers have to learn to use it in English, English speakers, the opposite.

[Jon345104]

I wrote Έχεις μία κοπέλα DL said to watch accent underlining μια