Blanche is characterized by her performative nature. She often hides the truth or does not let on what she is really thinking. To understand Blanche's jealousy, we're going to have to analyze her character and dig deeper into the things she says.

Blanche longs to be a high Southern lady, but she has lost everything. She is quick to judge Stella's small home and rough, lower-class husband. However, Blanche soon sees the devotion Stella and Stanley have for each other. They have passionate sex and a love that is deep enough to overlook faults. They are going to have a child together. Stella may not be living Blanche's ideal life, but it is a stable life.

Blanche does not have many options, and a simple yet stable life is looking better and better to her as the play goes on. She says

The poor man's Paradise—is a little peace

in scene nine, showing her desire for some peace and stability. She longs to marry Mitch so he can give her that stability, going so far as to meet him in the dark so he does not see how old she is. Mitch is Blanche's only option, as she has no money and Stanley is sure to kick her out soon.

We can also understand that Blanche longs for what Stella has by considering Blanche's past. The man she married was a homosexual and killed himself. This deeply affected Blanche, as she has not found a deep loving connection since then. She has had sexual encounters, but they did not mean anything. Considering her past, it makes sense that she longs for a love like Stella and Stanley.

Blanche is self-destructive, which she recognizes when she says to Stella

I never had your beautiful self-control.

It is possible for Blanche to be both repulsed by Stanley and yet also jealous of her sister's relationship. Blanche's past actions have narrowed down her options, which she realizes as she becomes more desperate in the play.