Vent and feeling negative for a while since my dad's talk around 2 nights ago

Vent: My dad is 65 years old and day by day, his mental process of thinking and comprehending is decreasing, more easily irritated and it would only get worse as he grows older. For example, he sometimes forget that he had already heated up the water for my shower and that I already showered, so he would heat up the water again and tell me to take a bath to which I had to after reminding him because saying no would anger him, plus, the already boiled water would be a waste. One day, my dad was asking me whether if I want <Meal A> or <Meal B> from a fast food restaurant we occasionally order from, so I answered with <Meal A> and said to him that <Meal A> has more meat than <Meal B> (with the purpose to give him an analytical information of which one is better to me). My dad replied "So which one you want!?" to which I answered with "<Meal A>" and then he said "Why did you have to say such nonsense?!" and he was in a bad mood for the whole day and waited for my mom to come back home because he planned to use her as an emotional punching bag (I believe what I said about <Meal A> having more meat is an analytical information and the intent is easily comprehensible, is it not? Am I wrong?). A meal is never delicious when I'm experiencing negative emotions such as anger or sadness, that have been internally experienced many times, but I still have to eat and finish the meal, otherwise, my dad will get more angry. I still remember which areas he smack me at, the most is the back of my neck, I keep feeling the urge to tear off the skin of that place to remove the emotional 'mark'.

I don't even trust his praises anymore because one time on a day which I still remember clearly, I helped to give him a drink, the amount is a half cup of water, I wasn't certain if the measure of the half cup of water I gave is correct or not, but he did a hum of approval and said "Good" when he saw the contents of the cup, so I ingrained that moment in my mind in order to remember that same amount to be correct and not be scolded for forgetting. But three days after, when I did the same amount, he scolded, angrily remarking and whining that "It's little" and then I argued back, saying that this is the amount I remembered that he said was good to which he answered "Ah, maybe I said that to save your face!" (to clarify it means that "He maybe did not want me feel shame at that time"), this made me feel resentful and anger due to feeling that my attempt to remember what was 'correct' from his seemingly approval was a lie, but at same time worthless especially when I heard him whispering "stupid" and when he said "I've learned something. I don't need your help anymore. I do it myself because you're stupid."

My Dad's Talk: Around 2 nights ago, he was talking about how a <specific nation> is superior, being smarter and hard-working than others which holds truth because that nation have commendable achievements. (For confidential reasons, I won't reveal what is that specific nation, but I'll highlight it as <specific nation>). I am a half-blood of a nation from my mom's blood which what he calls a <stupid, 3rd-level nation> and <specific nation> from my dad's blood. But the traits of the <stupid, 3rd-level nation> is more dominant in my personality. After he finished talking about the <specific nation>, he then talks about the future of the <stupid, 3rd-level nation>, how the people future will become barbarians due to the management and the corruption and that there's no future for it, calling the people to be useless with low IQ which made feel me depressed because I view that since I have the blood and traits, that he constantly points out, of the <stupid, 3rd-level nation>, I'll also be stupid and useless as well, I have no future nor will I achieve improvement especially with my clumsiness and the amount of mistakes I have. I simply sit and quietly listen to him, not doing anything else since to show I'm paying attention and don't want to be rude despite his topic affecting me negatively which is ironic since sometimes when I'M the one who talks about negative topics that I find interesting, he yelled at me to "SHUT UP!" which emotionally hurts me a lot. He gets to show his negative emotions as much as he wants while I'm not allowed to express my emotions at all like when I cry, he tells me "to stop crying, I don't like that." with no comfort such as hugs. My mom is more better in emotional support than him.

"Failure is the mother of success" Is what I seen constantly online, what my father said once and it seems to be the truth. But how can I accept my mistakes with ease when my father's attitude towards my mistakes is like he's condemning me, making angry shouts and whines with that negative expression of his and calls me insults, saying swear words in his native language?

I have a language exchange partner, and to me, I love how she tries to understand my psychology, my interests, being a listener and lets me talk what I feel like talking about which my dad lacks. The problem is that it's possible she may be a spy or a manipulator. Oh... But I wish I would have a genuine friend like that who isn't a manipulator...

I feel scared, maybe anxious whenever my dad is in a very bad mood and if he's constantly irritated, and we stay together everyday 24/7. I feel it's the wrong time to leave him, and I think the best time to leave is after he passed away from old age which is still a long time. My mom goes to work everyday except her day offs, I'm not allowed to go out at all if my dad don't permit it. I always seemed to have something negative to say about my dad every month. I don't have much people to talk to online, most of my language exchange partners seems to like casual things and doesn't have the tolerance to handle my negative moments. Fortunately, I don't get triggered as much as I did compared to the time when my dad started to have physical balance issues, but I would go into an impulsive outburst from time to time, it's rare, but it's still possible.