Hi I will like to answer your question, what book are you talking about?
Eres paciente pero divertido
"Eres" already implies the person it's talking to (you, in this case), if we wanted to make it formal, we would've used "Usted es" (You (formal) are)
if its only a few sentences you want he is sending a letter to ms luis about his exchange program, his work at an animal shelter, and his improved spanish
