They're kind of like mutual friends due to him being friends with Jessie.
Nathan considers her as a close friend, one of the reasons why he thinks that they're so 'similiar' is because they're both twins and the youngest of the twins. Although he seems to just want to have fun with her, he does care when she comes to mention things.
Nathan began to worry a lot for her after he and his brother found her breaking down because of her boyfriend.
As twins, they're very, very close. Nathan loves his brother a lot and he always tries to get Wyatt more excited than usual.