jughead saw when archie basically rejected betty, and is angered due to the fact that he believes she deserves more. he’s always liked her secretly and has never said anything since she’s always been so oblivious and in love with archie. suddenly they’re spending more time together while betty slowly gets more and more over archie, and realizes how into jughead she is. the scene with her writing in her diary is supposed to be about jughead, talking about how intruding into jason blossom’s room was a crazy thing that her love for jughead allowed her to do. afterwards she bumps into archie at the prep rally and finally doesnt feel a spark or romance between them at all, which is when she fully understands it’s jughead who she loves now, and the ending is betty looking supaa hot and jughead extremely interested !!