You are close he doesn't forge bonds so to speak. Its more of the fact that he is different and very human unlike the other sith. And yes Xalec is strangely attached to his master because well he was kicked down and neglected for so long that he considers the SI like a padawan would consider his own master. Since xalec is sith he himself can't put a finger on his own actions. Don't forget if you have only one diamond you are very afraid you will lose it and you value it more then someone with many.
I wrote a whole background story for my SI. There were not enough masters in the Jedi order so he was sent to be in the Agri Corp. The sith raided the agri corps because well tons of rejected force users. Those who didn't willingly agree to join the sith like my SI were taken to the slave mines and either died or were tortured until they agreed to turn dark. My SI never forgave the Jedi for the rejection and because of what he had to endure but he wasn't downright insane. So there;) Hope it helps! Anyway I doubt i'm going to write a whole story on it because I'm very busy doing other things. But I do love writing one shots so maybe I will go into detail on some of the things that happened to him in the future. Any particular requests? It would be easier to pm you if you had an account. Well Laters!