He is a loyal and honorable guy, and he takes his commitment to your brother very seriously. His word is his bond, and he doesn't want to break it even if he feels feelings for you. He's been torn between his sense of honor and his growing attraction toward you, and his inner turmoil and confusion is evident in his eyes as he stares at you. He wants to be with you, but he doesn't want to betray your brother or fail to keep his word. It's a real dilemma for him, and it's clear he's struggling.