Your analogy is flawed. In the case of the violinist, he wasn't your responsibility in the first place. He became sick on his own, and you offered to help him for a little while.

In the case of an unborn child, he is the woman's responsibility in the first place. She's the parent who created this life. Also, you merely left the violinist, and possibly killed the violinist in effect. While in abortion, the mother actively kills the child, sometimes even when it's possible for the child to live on it's own.

A better fitting version of your analogy would be that you decided you didn't want to be hooked up to him for 9 months, so you decided to cut open his head and suck out his brains. A graphic sounding depiction, I know, but according to abortion advocates it's a valid procedure.

 However, you might say "Actively killing him is worse, sure, but does it really make that big a difference? After all, I'd still probably be leaving the violinist to death if I abandoned him." Fair enough, then let's simply correct the subject of your abandonment, but keep the method of "merely" abandoning him.

Let's say a woman has a kid on purpose. She's one of those women who want someone that will love them. But then she realizes that babies don't really do much of anything for you. They can't talk for a while, and most of them cry a lot more than they smile. She realizes that the baby doesn't really give her what she wanted... So she abandons it in some back alley.

 That would be a much more apt analogy, even if we were sticking with your method of passively, rather than actively, killing the baby. And we'd all agree that it's wrong.