Heh, slowly turning to the dark side, are we, CVN? Well, it happens to all of us sooner or later, once you get past that period of ambivalence. (^o^)
As to your question though, I can obviously only answer from my own perspective. Being a bona fide 二次コン/nijicon (someone who prefers 2D girls to 3D ones basically), I can tell you for me, it's absolutely different when it's a character you really like and care about. I believe we went into the reason why real porn often ends up being an empty and disappointing experience, simply because you have no connection whatsoever to the person on screen. Sure, you get the release, but you don't get any emotional satisfaction out of it, much like with casual flings in fact. Indeed, there is a world of difference between 'having sex' and 'making love', not that you can get so many people to admit such. (T_T)
I suspected I was this way when I first clapped eyes on Flora from Jayce and the Wheeled Warriors around my late teens, although I obviously had no idea of the Japanese concept at the time. Truth be told, I've always found real girls unremarkable, but unlike my kid brother, who recently came out and admitted that he is asexual, I do have an extremely strong preference toward the female form, just often not the girl who is attached to it. I didn't truly accept it until I tried dating an actual Japanese girl in my late 20s, quickly realising I preferred the company of fictional ones. Tried again with an English girl in my early 30s mainly just to prove a point, and I've been alone ever since, not to mention infinitely happier overall. (=^_^=)
I won't bore you with the long psychological history of why I ended up the way I did, but suffice it to say, an amoral cousin (called "Karen", funnily enough, before the word was even a thing); many bad female role models in my family; horrible girls at school, college, work, etc. undoubtedly played a large part. For sure, I am almost willing to bet that other nijicons would have a very similar tale to tell. It's also undoubtedly why I prefer much more chaste feminine characters, at least on the surface, since it's patently obvious my emotional development in regards to the opposite sex is stunted as hell. (^_^;)