Please help me - I am an abusive father

Anger is a dark and almost constant shadow but last night I hit my 13 year old son. Hard. I slapped him 4 times across his face. Later I found there was blood in his mouth.I dont want to justify because there is no justification for what I did. But I do want to tell you what happened, I think there are 3 reasons. I need to get it off my chest. I need to be villified. I need help.The day was nice, our family of 4 [wife "A", oldest son "K" 13, youngest son "R" 9 and me mid 40s] were sitting watching TV. The boys started arguing and jumping on my wife [who was ill] and not listening to her requests to stop.I felt my irritation rise. "Will you guys just STOP! Do what your other is asking, you know she is now well!" Then the oldest turned to me challenging, shouting at his brother and using foul language.My irritation progresses to mild anger. Threats of punishment [taking away privilages eg XBOX etc] only partly get him to stop. My wife wants him to try some new clothes we bought for xmas and he keeps saying "no" then "ok, i WILL!". I need to leave the room, I go to the bathroom.When i return my wife is still asking him to try the new clothes on and he is still saying "I will". No longer at mild anger. Just anger now. So I shout at him to "get up and try on the clothes!". He responds with shouts and comments like "what are you going to fing do about it?". Im telling him "thats enough, go to your room", his response is "no, you cant make me, what can you do? Ill do what I fing want"Ive left anger and am now enraged. We get into a shouting match, the atmosphere is hirrid, my wife is trying to calm me down, R is crying, K and I are shouting at each other. His next comment is the one that I reacted to with violence. And I hit him. Hard. Harder than I think. Not just once, 3, 4 times across the face. He doesnt back down and keeps going. At some point I had him by the throat. My wife is screaming at us to stop. R is traumatised, sobbing. My wife tells K to get out of the house after she cannot get him to stop screaming and shouting.K goes to our neighbour wanting to phone the police but the neighbour brings him back saying he needs to talk it out with me and his mother. My wife is too angry with K and they start arguing again, then he leaves and doesnt come back for over an hour. Its a very cold winter night and all he had on was his jumper.I cannot look at him, nor he at me. He goes to bed without another word or look to each other. This morning he leaves for school. He will be back in a copuple of hours and I dont know how to talk this out. I dont know if I deserve to talk this out with him.Its the first time I have ever done that and the shame and guilt are destroying me. I haven't cried since the death of my father 10 years ago. But today I haven't stopped. I'm ashamed of myself and my self pity. I don't know what to do. via /r/Parenting http://ift.tt/2ipc7Ka