I think it would be fair to say that part of the reason Thomas & Reggie can get along is that Thomas treats him better than he earns. They are also very similar, personality wise, except their goals are more or less opposite. This is a generalization, obviously, and also I have insight into their personalities that you as a reader do not, but still… Thomas is the more sympathetic character of the two, but he’s no angel. Likely the main reason he’s nice to Reggie is that he’s using him. That said, Thomas can also see more of what makes Reggie human by being able to tolerate delving past his outer layers of jerk and getting to his soft jerk underbelly. I suppose that could be rewarding over time. If nothing else talking to Reggie helps sate Thomas’ almost pathological need to advise. He certainly needs guidance, even if he’s unlikely to listen.