...or we could simply look at what he said rather than speculating about the possibilities of torture and persistent emotional abuse.
There's a reason why, above, I said that this was also for the benefit of other people reading this thread and possibly not posting. The whole "fuck her feelings" thing as a default option is pretty sucky.
The simplest explanation is that the "what he did" was "try to win her back."
Let me tell you a story. I've got an acquaintance at this school--we'll call him K. The following is "K's worst rejection story," as he calls it.
K liked this girl, so when they were in her apartment alone, he kissed her. She said "I'm not okay with that," and they dropped it like it was the end of that, whatever. Well, so he waited a couple weeks until he got her alone in her apartment again, and kissed her a second time, and she pushed him off and said "no no no no no," and tried to get him to promise that he'd never do that again, or she wouldn't let him back in her apartment.
Well, K wouldn't have any of that. "I'll wait three years," he said, "but I'm not going to promise to stop trying."
He told me this story while laughing and laughing, and said he didn't feel bad because she had so overreacted to his advances that things had become simply ridiculous.
I'm not going to presume that the OP did something similar, but I'm pretty sure K owes this girl an apology, and "continued to pursue someone after she was disinterested" can come under a lot of different guises. How bout we don't make too many presumptions.
In any case, I simply suggest we look at this from the point of view of the current girlfriend. Imagine that you are the OPs current girlfriend, and he is preoccupied with that fact that the girl he used to want before he asked you out doesn't like him anymore, and is trying to get her to like him more instead of...for example, paying attention to you.
How would that make you feel?
If he did something wrong, then he has an obligation to her to set it right. It doesn't matter how jealous I felt, I'd take care of it because like hell I'm going to be an obstruction to my young fellow's moral behavior.
*shrug*
Putting it in terms of "she doesn't like him anymore" is a bit mendacious. She hates him. That's not simple dislike, that's something else, and if there's a story behind it I'd definitely want him to take care of it.