Why do you think it would bother him? It's the correct thing to call him.
You please your master and you make your master happy, but you don't please him or make him happy because he's your master, you do it because you like him? This is getting hard to understand.
I'm not a child, I'm a teenager.
...but it is your duty to fuck him, if that's what he wants. He's your master. You can still want it or enjoy it, but a slave's purpose is to please their master, however their master wants.
As a slave your life revolves around whatever your master chooses.