the question of who is the lover and who is the beloved in a male-female couple

This is a thought-provoking question. My first instinct is to say that the viewpoint character tends to be the lover because "lover" is a more active position to be in than "beloved." To have the viewpoint character be mainly the object of someone else's love seems like it would be stifling or oppressive.

But then I start wondering about real life... but real life has all sorts of patterns and I'm guessing rarely divides up easily into either category, or people are in both, etc.