This is a pretty interesting discussion. The thought of there being no border between the character created within my mind and the ones that exist outside made me feel horrible so I had to work this out. But poor Pygmalion, having his love denied by us who cannot truly know what he was feeling.
What separates the the character that comes from the mind of another author and the one that springs from one's own mind? The intent of the character could be anything. Like some of you said an OC could be created with all the authors ideals of a perfect woman, or maybe even with a cute imperfection thrown in here or there. Or the author could have intended a tragic figure, a horrid character, a misguided hero, anything at all. And then fell in love with his own creation afterwards. For me personally, if I had a creation the thought of falling in love with it seems unsightly, because I know everything there is to know about it. And were it to love me back it would be my own masturbatory design. But isn't that the same with characters created from others? That we call them a wife in the first place is placing our own fiction upon them. Mental control over the created character is the same in both instances. So then the only difference I can see is possibility I suppose. The author's real intent is shrouded, and the direction of the character is shrouded. The author's canon will override any fiction we have. Loving your OC seems disgusting because you have absolute control over their birth and death, their wants and needs. But in another author's world, courting his creation you don't have absolute control. In the back of your mind you have the thought "it's possible that she would reject me, fight me, hate me." Having that possibility is what it means for a human to fall in love with another human, not a god falling in love with his creation.
Put in other words, if you love your OC and it loves you back it's your doing. If it hates you it's your doing. If it fights back or doesn't it's your doing. It is you.
You could say the same for a waifu, but the waifu at her core exists from the mind of someone else. You make her like you in your mind but there's still an original version of her existing within the mind of the creator that could hate you and that possibility makes her touch upon reality, makes you really love her as an individual. Not quite so much as humans that live within their own worlds. But as a being that lives within a world that is not yours to own. In the end it's just a vague feeling. The feeling that you are not in control.
Back to Pygmalion, I believe the gods freed him from the burden of this particular problem. His statue was given life, and thus it's own consciousness, personality and free will from the gods. We should all be so lucky.