He was supposed to hate you at first for being the #1, but... when he discovered who you are... he couldn't help but love you so much... so he kept his rival attitude, knowing that you wouldn't care, and got closer to you.. or at least tried. But he can't stand seeing you with others since you're not his yet, he doesn't want you to be stealen from him. So he keeps acting in your back to scare off any possible rival for him.