Can I be kicked out of my girlfriends house if I've lived there over two years?

If, by kicked out, you mean just being put out in the street, the answer is no. You have established residence in the home and have to be treated like any tenant (note: I moved this from Family Law since it has nothing to do with Family Law).

But I'm going to guess that you have no written lease or agreement. That being the case, she can serve you with a written vacate notice that gives you 30 days to vacate (the amount of time may vary according to local laws -- ANY question on law needs to include your general locale as laws vary by area.). If you don't vacate by the deadline, then she can go to court and get an eviction order and have you physically removed.

So she CAN force you to move out, but you can't just be kicked out on the street.

In most states, no. Even if you are not on the lease/deed the owner is required to give u a written 30 day notice to vacate.