What did Stella do to cause Blanche to feel resentment? Scene one

Blanche asks Stella why she hasn’t questioned what happened to make her leave her position in the middle of a school term. Stella responds that she was waiting for Blanche to tell her, and Blanche assumes that Stella believes she was fired.

You haven't asked me how I happened to get away from the school before the spring term ended.

STELLA: Well, I thought you'd volunteer that information--if you wanted to tell me.

BLANCHE: You thought I'd been fired?

STELLA: No, I--thought you might have--resigned...