Misuzu is sad cause she doesn't have many friends
she only has Tomo and Carol and she both knows her 2 friends can easily leave her(Tomo going to Jun and Carol going to senpai or as we saw she is super friendly)
She thinks that her friends are fine without her but she wouldn't be fine without them, but she can't be Honest cause she knows her friends would be a lot happier if they are with other people and not with her.