Do you wanna know why you’ve become tangled up in all this mess and yet don’t know what it’s happening? It’s because you are only ever thinking about how you can be happy. Tell Adachi the truth? Are you an idiot?! The only reason you want to tell her is so that you can break up with her as soon as possible. Yeah, you might think that is the most sincere way, but you'll just unnecessarily hurt Adachi-chan. Even if you are the worst or whatever, if you have still have the will to go out with Adachi-chan, you need to hide your feelings for Hatori and act accordingly! But if you can’t erase your feelings for Hatori, then throw away Adachi-chan and hurt her for real.