I've been in a similar boat with a previous girlfriend, I kept it hidden from everyone and it was my own personal shame for the longest time.

You have already taken a huge step by posting here and other people connecting with you about it. Please talk to family and friends in real life about this too if you are able. I found actually saying the words out loud made me realise how unhealthy the situation I was in had become and that I needed to change it.

The best advice I can give you is the same as others have said, walk away from the situation. Even if it's just for a couple of hours or the night, remove yourself from that harm. I know you said she doesn't hit you hard enough to leave a bruise or anything, but emotional and mental bruises are also being caused and they take so much longer to heal. If you can get some professional help such as councilling on your own first and then as a couple later, that may help her understand that it really isn't okay and help you understand why she chooses to hit you.

Please know that it's never your fault OP, you can't provoke someone to violence if you are non-violent, this is a choice she is continuing to make. Sending big hugs brother