When Simon goes back to school on Tuesday, Abby is waiting for him, worried. Simon explains his parents took his phone and grounded him. Nick walks up as Abby apologizes, thinking it's her fault, but Simon insists it was all his fault. Suddenly, he notices that Nick and Abby are holding hands, and suggests they didn't miss him too much on Friday. Later, Abby tells Simon that she and Nick waited a while to see if Simon's parents were going to let him back out, but everything ended up being fine for them.
Now that Nick and Abby have decided to admit their feelings for each other, it suggests that they were willing to have the conversations that the rest of the friend group has been unwilling to have. The fact that they both seem happy with the outcome shows that there's a lot to gain from having these tough conversations and being honest.
Bram and another kid had birthdays over the weekend, so there are two sheet cakes at lunch. Simon is confused, however, because Leah isn't there and wasn't in classes either. Another girl tells Simon that Leah is at school, but Simon is worried anyway. He notices her car in the parking lot over the next few days, but can't figure out where she is. On Thursday, Simon finally catches Leah coming out of the bathroom. She asks if he, Abby, and Nick had fun on Friday. Simon apologizes, but Leah isn't willing to accept it. Simon walks away and Leah calls after him that next time they hang out without her, they should text her pictures so she can pretend they're still friends. In tears, she turns back into the bathroom.
When there are sheet cakes but no Leah, it suggests that she may not be the one responsible for the sheet cakes all the time. This would mean that Simon has been making even more assumptions about the people around him in an effort to make things seem the way he wants them to be. Leah rightfully sees her exclusion as something hurtful and mean, which will mean that if Simon wants to fix their relationship, he'll need to figure out a little more who Leah is and how to be a good friend to her.