This book is full of thwarted love. How is this true for the characters?

You are correct, the book is full of thwarted love but all the major characters experience this. You need to submit each character you want one at a time.

Consider Baby Kochamma. She is Rahel and Estha’s grand aunt, her grandfather’s younger sister. When she was young, she fell in love with a priest, and converted to Catholicism. She joined a convent, thinking it would bring her closer to her love, but when this fails she returns home, resolving to stay celibate forever.