Most Helpful Girl
You dumped her because you felt nothing for her so what's the problem? You don't own her she can do whatever she likes with whomever she likes and the guy already did the nice thing he didn't have to do which was ask you If you were ok with it.
You can't just change your mind and wreck their relationship because you don't like it anymore. A month isn't much time, it doesn't mean she's still in love with you she might just want to take things slow and do things properly with him. The guy could be lying to try and make you more comfortable with the relationship between them by saying they haven't had sex yet even if they have.
It's none of your business anymore and I don't know why you even care if you have no feelings for her
Most Helpful Guy
there is no telling if she is over you if you don't ask her yourself, if it bothers you do you still have feelings for her is there a chance you could work things out and get back together with her? if not there is not really anything else you can do. I personally wouldn't date anyone my 'friends' had previously dated. it doesn't seem right especially since I knew all the problems between them both. I think if you want to get back with her then maybe you should talk to her and see what she says if you don't want to get back with her. there is nothing you can do and you just try to just let it go. Wish them the best and move on.