Weight is a problem ?

So I'm 20 , five one , 144 pounds with hips and butt . My body isn't the best I don't work out I don't tone anything and I have a junk food tummy well you know that pudge and my bf doesn't like it . He says he doesn't care but he's always grabbing on my fat and calling me a fat ass when I eat a lot at his house (he always a says he's playing but I don't like it  ) .. I don't have the motivation to exercise but I wanna be slim for him what can I do to be slim ?