@Travis20,
Travis, you're right.
This shouldn't have happened to you.
Your girlfriend too advantage of you. She did something very wrong. I would say she sexually assaulted you. In some jurisdictions, she would be considered to have raped you.
If you can, speak to her about this very seriously. Make sure she understands that what she did was wrong. If she doesn't understand it, you have to consider if she is someone you want to be in a relationship with.
If a friend of mine did this to a man, I would tell her that she needed to seek counselling.
If this was done to a male friend of mine, I would ask him if he wanted to press criminal charges against her.
I am sorry this happened to you.