The problem that the characters have with identity runs throughout this play: It is one of the areas that I really like.
Spoiler:
Sergius acts as a focus of this theme through his relationship with Louks. He is drawn to her, and cannot overcome this bond through the other {false} layers of identity he uses when speaking with Raina.
"SERGIUS (coming clear of the table and drawing her with him). I
am surprised at myself, Louka. What would Sergius, the hero of
Slivnitza, say if he saw me now? What would Sergius, the apostle
of the higher love, say if he saw me now? What would the half
dozen Sergiuses who keep popping in and out of this handsome
figure of mine say if they caught us here? (Letting go her hand
and slipping his arm dexterously round her waist.) Do you
consider my figure handsome, Louka?"
Louka actually does love him but is grounded in reality:
"LOUKA. Well, you see, sir, since you say you are half a dozen
different gentlemen all at once, I should have a great deal to
look after.
SERGIUS (charmed). Witty as well as pretty. (He tries to kiss
her.)
LOUKA (avoiding him). No, I don't want your kisses. Gentlefolk
are all alike--you making love to me behind Miss Raina's back,
and she doing the same behind yours."
When Sergius slips into a self-satisfied, "genteman" persona to put her down, Louka immediately points up his hypocrisy:
"LOUKA. It's so hard to know what a gentleman considers right. I
thought from your trying to kiss me that you had given up being
so particular."
and she senses who the "true" Sergius is:
"LOUKA. Ha! ha! I expect one of the six of you is very like me,
sir, though I am only Miss Raina's maid."
Louka has complete self-awareness, knows what she wants, and takes the necessary steps to get it.