I'm sorry you've been having such a rough time. It's hard for me to know if he is a sociopath. It's always very hard and inaccurate to diagnose someone else third-person. There could be lots of ways to diagnose him. The most telling things in any diagnosis, though, are the things that a person says in reference to himself. For instance, his asking you whether you think it is possible that someone would not have a conscience, his saying that he does what he wants, or his saying he will fuck you over -- those are clear indicators of sociopathy because they show both his self-awareness and his acknowledgment of his irregularities. If he's not a sociopath, he is a completely self-absorbed asshole and you shouldn't be sorry at all if you hurt his feelings. If he is a sociopath...
Loving his mom and dog are not necessarily inconsistent with him being a sociopath. I love my mother more than anyone else in the world. I am also very sweet to her, always buying her things, giving her money, taking care of her, but I do not say things like "I love you," either. She's my mother. He's a source of unconditional love and acceptance for me, and is in many ways an extension of me, so it makes sense for me to maintain that relationship. Same with the dog for him, probably.
When I tell people I love them I really mean it in that moment. I told someone today that I loved them. What does it mean? It's a very childish, fickle infatuation. I also sometimes hate this person -- quite often, in fact. I feel like this person secretly judges me, and pretends to be all understanding without truly accepting me. I behave towards this person similarly to the way your boyfriend behaves toward you. On the one hand there are the moments of awe and affection that I feel for the person. On the other, there are the feelings of rejection, boredom, disinterest, selfishness, etc. that motivate other behaviors.
This guy seems particularly bad because he is so conflicted about himself. Although he may be unusually insightful and self-aware, he doesn't understand himself. He is probably both in awe of himself and fearful of himself. He seeks to control others because he does not feel like he has control over himself. He warns you that he will fuck you over not because he wants to, but because he fears/worries/knows that he will. His asserting that gives him the illusion of control over the situation when really he feels like he only has predictive power, not power to change outcomes. He says he does what he wants, but he's really just trying to own the fact that he does what his impulses direct him to do -- then play it off like it is all part of some master plan of his. His bravado in saying he "does what he wants" is his way of trying to pretend that he is making conscious, reasoned decisions in accord with his values and preferences instead of being a slave to impulses he neither understands nor can control.
I'm not surprised he is in his early 20s. Sociopaths are the absolute worst in their late teens and early 20s. They're the equivalent of teenagers with raging hormones. Late teens and early 20s start the sociopath's first real tastes of freedom and power, which they begin abusing like a kid on meth. Once it gets to a certain point of excess, and the first real, lasting damages to their lives occur, they will then withdraw for a period of introspection, which will last until they gain a certain level of understanding and self-acceptance. At least this has been my own experience and the experience of many sociopaths I have known. If he doesn't go through any of these phases, then he will stay as he is forever. But how could he? Really, it doesn't sound like his charmed life will stay that way for much longer.
He's not a bad person necessarily, but he certainly has the potential to be and has definitely been acting like one. Don't feel bad for allowing him to feel the consequences of his actions. He will not change for the better until he feels like he needs to. He will not feel like he needs to unless/until his current modus operandi ceases to function.
I don't know what's up with his impotence. It could be that power/control is what gets him off, or that he has come to associate sex with things that you would consider abnormal. If he wasn't gaming you, or not as much as the other girls, it could be that his difficulty stemmed from the lack of power and control he felt in the relationship. But that's just a guess.
You cannot change him. He will not even change himself if he thinks for even a second it will work out with you without him changing. It may be that you have already communicated this sufficiently to him, i.e. that things will not work out ever between you, at least not as they currently are. His avoidance of you could be him sulking or trying to get back at you for this, or it could be his tacit acknowledgment (albeit not fully conscious) that you mean what you say and that he can no longer game you. I'm sure you would prefer it to be the latter, so feel free to think that way -- it's at least plausible. In any case, do not be afraid of hurting his feelings. Even if you did hurt them, he deserved it a million times over.
Hope this helps.