Thing is, you can do whatever you like and go to jail for it after 18. But what you can't do is get financial support from parents who are using that as the last resort to keep you as their baby. Your parents are greatly at fault. Do you need them for food and shelter? If so, you need to state the position calmly, and abide by their decisions, otherwise you are up the creek without a paddle. Have you given them reason not to trust you? If not, remind them them that you have been trustworthy. Does your gf love ylou as much? In which case she will wait for you to come back from hols and be all a-fire to carry on where you left off.
Of course, if she was very naughty and willful and over 18, she might take a tent and camp near your folks holiday home......