|This was the best image I could find of the Boltons|
from Episode 8. What could it be about them that makes
people so unwilling to honour them with screen-caps?
(TV spoilers below, all book spoilers have had their heads crushed like grapefruit)
I mentioned two posts ago how the Greyjoy storyline in this season is basically all about how it has been swallowed up entirely by the Boltons, with Theon completely under their control and Yara cast almost casually aside when she attempted to intrude. In that post I talked about Theon's awful relationship with his coldly ambitious de jure father and his coldly courteous de facto one, and how those experiences lend an air of tragic irony to Theon having been beat to the point he's fallen in love with his newest figure of authority. After years of being the heir to the Iron Islands and the best friend of the heir to Winterfell, Theon has finally found what he believes is his place at the side of the vicious sadist who tortured and mutilated him.
It's worth looking at this dynamic from the opposite viewpoint, however. There seems every chance that Ramsay would have treated any prisoner to fall into his hands equally horrifically (if his approach to dumping girlfriends is any indication, at least), but that doesn't mean there isn't a peculiar and specific bond between the two men, or no reason for Ramsay to have that little bit of extra motivation this time around.
Understanding why Ramsay might have just that little bit more psychopathic violence in him that usual, we need to consider what drives him. Like his fellow Snow, Jon, Ramsay's entire worldview stems from his status as a bastard. Obviously the to have taken very different paths, almost certainly due to the the very different relationships they have with their very different fathers. From the loving but inflexible Eddard Stark, Jon learned the importance of wisdom and honour and wishes nothing more than to prove a bastard can be as good and trustworthy a man as anyone trueborn. From the calculating, even sociopathic Roose Bolton, Ramsay learned different lessons. Let's consider the source, then. I think the kindest description of Bolton's approach to the game of thrones would be "ultra-pragmatic realpolitik". We see this in his use of Ramsay to take Moat Cailin. If Reek had failed and Locke returned with Bran in tow, one wonders if Roose would have written his tracker into his will instead. There's also Roose's approach to his new marriage, picking the fattest batcherlorette on offer in order to maximise his dowry. These qualities are even more obvious in the books, in which it is revealed that not only did Roose switch sides the very moment he concluded the Young Wolf was going to lose, but that he strongly suspects Ramsay is responsible for the death of Roose's trueborn son Domeric. Embracing your bastard son after concluding he killed your son, his own half-brother, might seem ludicrous to us, but to Roose it's the only sensible option. With Domeric gone the most suitable choice of heir is Ramsay, and there ends the discussion.
Until he is legitimised, though, Ramsay knows two things: power is always the ultimate goal, and his bastard surname is an impediment to that goal for as long as he bears it. For Jon, legitimacy was an impossibility he forever tried to prove to others (and himself) that he didn't need. For Ramsay, it was a carrot forever dangled in front of him so as to keep him useful.
How this plays into Ramsay's sadism isn't clear - we have little available with which to consider whether Roose shares his son's sadistic streak, or whether he would simply consider it a distraction - but reasons abound as to why he might focus so much of his vicious attentions upon Theon. This, after all, was a man not only trueborn, but heir to Pyke, one of the ten most powerful castles in Westeros (Theon is probably wrong that no house can look down on the Greyjoys, but there certainly couldn't be many that could beat them in a straight fight). Hearing Theon bleat about how hard it was to have a father who never showed him any affection must have struck Ramsay as massive ingratitude. Worse, it was weakness, the same weakness that left Theon unable to even track down and kill a crippled boy. The crowning insult was Theon's lament about realising too late that Eddard Stark was his true father in all the ways that mattered. Theon gets a name, a direct line to a formidable castle, and two fathers, neither of which Ramsay could imagine treating with the same attitude of "I guess since you're alive I can use you" Ramsay apparently received from Lord Bolton.
The assembled effect must be like pouring salt into a lifetime of raw and open wounds, and Ramsay's response is to simultaneously punish Theon for what he values so little, and to strip those things from him completely. Obviously, he tears away Theon's name, but that isn't enough. Ramsay is all too aware that what others think of your name is at least as important as what you think yourself (another trait he shares with Jon) . And so in the process of breaking Theon, he cuts off Theon's cock. Not just because he's a vile and bloodthirsty monster, and not just because he needs a horrible paperweight with which to underline his resolve to the Iron Islanders. Ramsay did it to separate Theon fully from his bloodline. Theon is Reek now, and even those who don't understand that will never see Ramsay's pet produce another Greyjoy. He is now further from his father's family line than Ramsay is from his, with the added irony that Reek loves him for the punishment he's inflicted as much as Theon hated his family for the gifts they gave him, simply because they went slightly awry. The fact that this deconstruction of Theon ultimately gains Ramsay some of those very same gifts is merely the icing on an exceptionally unpleasant cake.
So, with that cake served, what happens next? We probably can't hope for Ramsay to become any less unspeakably unpleasant anytime soon. even if his sadism is tied directly to his inferiority complex, such deep-rooted neuroses don't simply disappear once their original causes do; Nixon taught us that. Which rather raises the question of how much long longer Theon can enjoy the rank of amusing pet. Will Ramsay keep him around until the squids are finally cast out completely from the north ? Or will his new status as heir to the Dreadfort remove his need to use Theon as an infiltrator/bargaining chip?
And if not, what happens then? When Reek ceases to be amusing, will Ramsay return to the tried and tested methods of unspeakable torture? That's what Ramsay Snow always loved. But Roose Bolton would be more likely to quickly dispatch Theon the very instant he ran out of potential tactical uses. So what will Ramsay Bolton do? Is there anyone among us who can tell? Is there anyone among us who would truly want to find out?
 Actually, this is incomplete, because it fails to take into account the self-loathing both of our northern bastards have cultivated by internalising the opinions of others. What you think of yourself probably outweighs how others view you, but the former is so regularly and insidiously infected by the latter that the distinction often becomes irrelevant.
 As usual the show has been utterly awful at explaining the overall status of the various forces in play, but by this point in the book, Ramsay has reduced the Greyjoy holdings in the north by about half.