It’s a love/hate relationship with Abby at the scene where Abby finds Ellie's group at the theater. The reader is Ellie's age and had become like a brother to her/son to Joel. Back when Abby killed Joel the reader fought with her and lost but to add insult to injury, she kissed his cheek afterwards in mockery.
Unfortunately this had the unfortunate effect of causing the reader to start developing feelings for her and Abby couldn't help but respect his bravery and will to fight, so when she has the gun pointed at Ellie the reader tackles her but she pins him instead and it results in them kissing is a rush of emotion. Much to Ellie’s horror.