Physical & Emotional Abuse Support Group
Abuse is a general term for the treatment of someone that causes some kind of harm (to the abused person, to the abusers themselves, or to someone else) that is unlawful or wrongful. No one deserves abuse, period. Abuse can be emotional, physical, or sexual.

Seriously, all that you describe is perfectly normal and incredibly common among victims/survivors of abuse.
First of all, why didn't you spot the signs? I believe my ex was also probably a sociopath (he fit the signs, but I'm not qualified to diagnose of course) and in among the reading I did was a page about how to avoid relationships with sociopaths. I can't remember where I found it now and so can't provide the source, but it was someone well respected. The simple answer to how you avoid getting into any kind of relationship with a sociopath is ... you can't. They are good. They know how to find your weak spot, they are predators, knowing just how best to bring down their prey. If they showed their true colours at the start, of course you wouldn't fall for them. Yes, in hindsight, we can all see the signs we either missed, minimised or ignored (or that they had what seemed like a totally legit explanation for), but those things can really ONLY be seen in hindsight. So please stop beating yourself up for what none of us was able to avoid. There are a lot of very smart, successful women and men who've had to find their way to this board, because they also didn't see the signs.
As for why he tried so hard to keep you - you were obviously still of use to him. And yes, control is at the absolute heart of what abuse is about. Did you notice the push-pull? Most of us have been through at least some of it. If you want to go, he wants you to stay. If you want to stay and work things out, he couldn't give a crap. They just want to control you and your emotions, make sure you don't make any decisions for yourself or, if you do, make sure you can't carry them out.
I understand all the questions, I think it's part of processing. But you CAN drive yourself crazy with it-because some questions you will never really know the answers to. It is helpful to question to a point-and that points comes when your head starts spinning. He did those things because he got something out of it. It made him feel powerful to yank you around and push your buttons. He did *something* (doesn't matter what lick that something was) and you reacted (and the reaction didn't much matter either, as long as the reaction included engagement)-HE did that. Abuse is always all about power and control.
Abuse chips away at your ability to trust your own perceptions. THIS is one big reason why you doubt yourself in that relationship. Another reason is that we all want a sense of control over the unpredictability in life-sometimes it's easier to accept we cause BAD things to happen, even if it causes guilt, than you accept the terrifying thought you can do everything right and terrible things can still step out of the dark and get you. You also spent all that time minimizing all that happened to you so you could psychologically survive the abuse. You minimized it so the true horror of it could be put away in a little box in your mind until you were ready to take it out and deal with it. It's not that anything is wrong with you. All of that is a perfectly normal reaction to trauma.
I also agree with cant that the questions are good up to a point. For me, the point at which the questions stopped was not when I got the answers (I'll never have answers to all my questions) but when I realised that the questions were keeping me constantly trying to get inside his head. I realised that wading about in there was like wading about in a stinking, foetid swamp. So I waded out and spent the time and energy on me instead, on the reasons I did what I did, on the reasons I accepted his treatment of me. In doing that, I do NOT believe I "trained him how to treat me", I do NOT believe I was in any way responsible for his treatment of me. Some of my behaviours/attitudes made me easier prey, nothing at all that I did made him a predator - that was HIS choice.