Is It Okay To Date Someone My Friend Used To Date? [THE SCENARIO]

Today's topic came from a young woman who wrote:

Dear DJ Supreme,

There's a guy that I really like, I gave him my number one day and we have been talking ever since. After realizing that I was really feeling him I told one of my friends about him and it turns out that they used to date!!! My friend insists that she doesn't care but I can tell that she kind of does by the way she tried to hate on him. Would I be wrong for continuing to talk to him or should I leave him alone?

Thanks!