How does Nicholas feel when he discovers Paige with Max at his parents' house?

Nicholas lets himself into his parents' house and hears Max's laughter from the nursery upstairs. Nicholas crawls into the room to surprise his son and finds the surprise is on him. Astrid is there, and so is Paige. Nicholas is jealous that Paige can make Max laugh so easily when it took him weeks to learn how to please his son. Nicholas thinks of a morning when Paige got up early to make his lunch and she wiped her hands on her nightgown when she thought Nicholas was not looking. Paige had not gotten up to make his lunch since Max was born. That is when it hits Nicholas that Paige has not come back for Nicholas; she has come back for Max.