I don’t know if I believe this is even true. If it is then OP “it was just piss” and “piss is natural” is clearly not working, I hope you can see that. I know its hard not to get defensive when people are calling you out but you have to reflect on what people are saying. You were sexually assaulting your girlfriend.

Fetish or not, what you did is wrong. “Natural” or not what you did is wrong. You’re still young so you have an opportunity to learn and grow from this situation. Try to do that instead of being obtuse.