What Wakeup said.
I don't know if your girlfriend lied at the beginning about loving sex - or if she's simply not into you. But either way, you have a big problem which isn't going to go away.
How long have you been together? Did she ever enjoy sex with you and if so, how long did that period last? Is she confused about why she feels as she does....or does she think this is normal?
Lastly, your girlfriend is right when she says that if she doesn't feel like sex then she's not going to feel like foreplay. Nothing worse than someone fiddling around down there when you're not into it.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.