From what I understand, an NFA cannot have backtracking. For an assignment I have to have strings that always end with ab's, and I have come up with this diagram. However, I still struggle with the difference between the two and because of the backtracking, this is considered a DFA (I think?) Can someone suggest me how to tweak this into a NFA?
It's deterministic. You can tell because each state has at most one outgoing arrow per symbol. This means that, no matter which state you end up in, the machine determines which state you go to next, so there's no choice, and hence no need or possibility for back-tracking.