It had seemed like Sin thought of him a little more as a partner but perhaps he still didn't trust Boyd despite the fact that he'd saved his life. Whatever the case, something about seeing vulnerability in a man who otherwise exuded such strength caught Boyd's attention in a way he hadn't expected. That glimpse of Sin seemed so elusive compared to the way he conducted himself on a daily basis.
Something in Boyd reacted to it; something that felt a connection and made him want to see more of that side of Sin. It made him not want to look away from the screen so he wouldn't miss another fluctuation; another moment of openness in an otherwise guarded face.