you are not being treated fairly. you gave your gf an honest answer to a question she chose to ask you. if you're experiencing this much stress now you may want to consider the longevity of your relationship.

I think you need to give up trying to make your mom happy. Obviously I can't speak on how she's treated you your whole life but I really think you need some independence from your mother.

You seem to feel anxious about not upsetting her when really it's not your fault that she chooses to react the way she does, and you shouldn't have to feel like you need to lie or alter yourself to avoid her reactions.

I think you should focus on yourself and your life and your relationship and have some time away from your mother. I'm sorry she treats you like that, and I'm sorry your father doesn't stop her.