Blanche states in scene 5, "I want Mitch—very badly [emphasis added]," but she does not necessarily want to impress him. She actually states, "I want to deceive him [emphasis added]." It can be argued that she barely sees him as a person. At the play’s end, Blanche utters the now-famous line, "I have always depended on the kindness of strangers." Mitch is another instance in her pattern of searching for others to rescue her rather than strengthening her internal resources.
In talking about their upcoming date, Blanche actually speaks only about herself. She talks about the ways she has misrepresented her age and sexual experience: "he thinks I’m sort of—prim and proper." She does not speak about any of his attributes that she appreciates. Rather, he is a vehicle for her to escape Stella and Stanley’s apartment: "If it happens, I can leave here and not be anyone’s problem."
Mitch, clearly, is not a person to her; he occupies the position of yet another shining knight. She therefore distorts her own image by lying to him, as well as to herself, in her attempt to fit the picture of the two of them together. When he uncovers the numerous fibs she has told him, she counters with her own logic, saying, "I never lied in my heart." Even at this late stage, she cannot and will not admit responsibility for her actions.