She left because she thinks his life is about his kid and his career and she feels unnoticed and unrespected. He just gives her superficial kisses, no conversation shown. In the end she leaves what she thinks was more important for him than his family and shows him what he lost through setting his priorities on himself and not at least a bit on her.
Is that so hard to see since the video really throws it at you? I rather ask myself how someone could not understand the message?
(Beside somebody is a fangirl and goes like "Whaaaaaat hes soooooo cute, how could he have left hiiiiiiiim" - in which case I´d say this person really is fucked in the head or a teeny girl)