Matilda’s act of sacrifice could indicate her selflessness. However, given her history of deception, it is more likely yet another concealed attempt at seduction. It’s clear that Ambrosio’s ability to suppress his desire for Matilda has weakened considerably since he first learned the truth about her identity, so perhaps Matilda is merely faking her illness as part of some calculated scheme to seduce him by preying on his emotional vulnerability: if Matilda has truly sacrificed herself so that Ambrosio may live, surely returning her romantic advances is the least he can do to repay her.