why did Abby and McGee break up?

Abby and McGee have never been together, they like themselves, especially McGee, but they have never had it going on......
Am so sure....

In season middle or near end of season 1 they went on a couple dates and definitely were together for a short time. in season 3 "bloodbath" there is a reference that abby's toothbrush had been left there. but it has never been said or i haven't found why they broke up.

They broke up because Mcgee wanted mais out of the realtioship but Abby was fine were they were