Who actually this devil is and what does she want?

Love is a cruel goddess, who like all deities, wants to possess the whole man and who is not content until he has sacrificed to her not only his soul but also his physical self. Her cult is suffering; the peak of this cult is self-sacrifice, is suicide.

--Bauer

Who actually this devil is and what does she want?

Your soul. Evil has no life of its own, it wants yours.

And what does it do with all the souls?

It doesn't do anything. It just wants to have them. It can not *be* so it is driven to possess. There is life in be. Death in have.

--xman