I think Adam would be very careful with Perer that day, knowing how much his birthday means to him.
Pete probably doesn't really celebrate - he'd more likely spend the whole day silent, wearing headphones and barely engaging in conversation.
Nikki would convince the others to make a surprise party to cheer Peter up in the moment, give him gifts, and spend time with him. He would appreciate it, but with a hint of sadness.
After the party, Adam would suggest going for a walk and they'd have a nice heartfelt chat.
Adam would feel a bit awkward giving him a gift, even if he really wanted to: "what if it only made Peter more upset?"
Still, he'd try to cook something tasty for him c:




















