I think it means that she seriously wants her space
maybe she just feels having a boyfriend right now is too much and she feels that she can't give enough time to her boyfriend and instead of hurting him she decides it's easier for her to let go of him
Sometimes it could mean that she still likes/loves you, but the relationship is just too much. Maybe she has lot of her mind, and just wants time for it to settle. There is alot of different reasons why she could have said that.
It depends on the girl. It could mean she found a new guy, it could mean she lost interest, it could be shes not ready for a relationship, it could mean she just needs her space!
So many possibilities...don't worry though, we love you
If I said that I would be saying it because the guy was taking things too fast and I want a break. It doesn't mean she doesn't still want to get back with you at some stage.