Take a second and look at Lydia.
How she looks at Stiles as he’s expressing how he was worried about losing Malia.
Her face looks filled with surprise, sadness, anger, maybe even guilt.
Lydia knows that’s how Stiles used to be towards her.
She’s realizing he has moved on.
She came to the conclusion that she didn’t take advantage of how he used to treat her.
She is just now beginning to realize her feelings for Stiles, just as his feelings have turned towards someone else.
Do you ever think about how lottie waited for harry, n how she was young when she met him and prolly learned by example how to treat him, n hes prolly important to her because he is a beautiful person but also cuz hes so precious to her older brother