Taking anger out on my dog

Im 19, lving with my bf, and our small dog.
Ive owned dogs all my life but this is the first dog ive had on my own. We got him at 8 weeks and i loved him ! But once he got a little bigger, i started getting this deep burning anger whenever he would do something bad, and i would hit him or give him a kick. Every time he chews something up i drag him out from under couch where he hides and hit him once hard. Whenever we do tricks and he doesnt understand he gets freaked out and runs away under the couch so i get angry and do the same. Sometimes ill pick him up by his neck or his fur. If he starts barking i grab his snout. Once he tried to bite my horse so i grabbed him and hit him 3 times as hard as i could. I dont WANT to do this, i feel so guilty after but its like in the moment i dont care and cant stop myself. I cant get rid of him my bf loves him so much and i bought him for a lot of money from a breeder and its very selfish but its not money i can just throw away and i wanted my bf to be happy i had no idea i would do this to an animal ive always loved animals and i really do love my dog!
Idk what to do i feel so ashamed my bf knows i do this sometimes and he tries to help me but he doesnt know how bad it really is. Im surprised my dog doesnt hate me yet he is nine months old and its been happening probably since he was 5 or 6 months old .
I was not abused in any way as a child, but i was bullied and have self harmed in the past. I suffered from an eating disorder previously for around a year. But i have never felt anger like i do with the dog .

Um, a dog is very much like a child. Spanking, hitting or physically punishing a child's bad behavior is not terribly effective. What is more effective is to send the child to his room for an hour or two to contemplate his bad behavior and learn to apologize for it afterwards. It's equivalent to being sent to the doghouse. So, likewise take the dog by the collar and take him outside to the back yard or back porch, say "bad dog" in a firm voice, and ignore him for awhile. A dog doesn't like being by itself all day. Enough of those "outs" will get the dog to make a connection between bad behavior and the "doghouse" and as it gets older, it will recognize what's not acceptable behavior.

I shudder to think what if this were your real kid who acted up...get a handle on your temper, girl.

I am not judging you, I can see you hate what you are doing, but please try and think differently. Your dog is just a typical dog doing things all dogs do, dogs do have a fascination with chewing.
I bet your dog has such a lovely soul, he will be so loving and loyal to you. Think of his feelings and how much hurt he must have felt and feels when you hit him. Don't do it any more, give him cuddles and make him happy, he will be your bestest friend in the world.

I had a stroke about 21 years ago. At the time I had a dog who had grown up with me who loved and trusted me, who I loved and cared for. The stroke has left me incapable of love, which my dog sensed, and she became a very lonely unhappy dog because she no longer had me as her mother. I also dropped her and maimed her, so she needed a lot of help just to get around, help which I did not want to give because the stroke has left me disabled and chronically tired, so she became a nuisance for me to look after. I treated her cruelly roughly, unjustly and irritably. The last 4 years of her life were miserable, confusing and lonely. Eventually I had to have her euthanised due to the disabilities that I caused her. I have never forgotten what I did, nor come to terms with it. I cry most days over the memory of what I did to her. I cannot ever imagine that I will get over it, because she no longer exists I can never make it up to her.
For you, do you want to suffer misery and guilt for the rest of your life? Maybe, if you feel that you are going to lash out at your dog, remove yourself from his presence. Or is there someone else who can care for him for a while, until you can get your feelings sorted? Even if your dog starts loving someone else instead of you, that would be better than you harming him, so that he can never even like you