Why is Tita conflicted about her engagement?

Tita also feels anger as she tries to redirect her former passion for Pedro. Now engaged to Dr. Brown, Tita has no patience for Pedro’s attempts to woo her. She urges him to be loyal to her sister who he agreed to marry and respectful to Dr. Brown, who Tita intends to marry. However, Pedro’s insistence on bringing up his love to Tita frustrates her immensely.

Still, a strong physical attraction and response exists between Pedro and Tita that does not exist between Tita and Dr. Brown. A stare alone from Pedro causes Tita’s entire body to heat up. This suggests that Pedro is the oxygen Tita needs to light her matches, not Dr. Brown.