Every interaction focuses on her. She kisses him on the cheek; he just looks at the camera. She kisses his picture during the "shaving" scene. She watches him walk down the street and talk at her on video… the only personal expression element of the "story" is his. She simply receives it. When she's upset, the focus is on what he does to her — the arm, the drawing, she receives the apology but never participates in a make-up.
It looks like the boyfriend is a prop. But the joke is it's that the woman, the focus of everything, is the prop, because it's from the boyfriend's PoV and she's just this super-emo recipient of his actions. Except when she's delivering outsized love he doesn't return (omg! the fawning! the kissing! the posing! the crying! all while he looks on and, if he expresses any emotion, just a smirk).
And if you don't believe about the childlike thing, it's capped by the scene at the end where she's hiding under a sheet with one stripey sock sticking out, a direct echo of "kids reading under the covers when the lights are out." No adult does that.
So: the video is assuming you, the male viewer, are a narcissist (everything is about you, and ps, you don't have access to real feelings), and that the object of your affection (not "girlfriend" because that implies a two-way street) is a baby.
This video is insulting to everyone. Sheesh!