I feel horrible for slapping my wife by accident?

We have been married for two years. She is 21 and Im 30. We argue alot and unfortunately its because of me. She knows I cheat on her. I admit it to her though and I tell her that I love her but I do have sex with other women from time to time but that it doesnt mean anything. I know I shouldnt but its just something Ive always done. Well she found condoms in my car and came into the house yelling and cussing me out and crying and being hysterical. She was screaming that shes sick of me cheating on her and that shes tired of taking all this crap from me. She was pushing me so I went to leave but she blocked the door and I yelled at her to move and she punched... not hit... but Punched me right in my eye HARD. Then she kept shoving me and crying and I suddenly turned around and slapped her in the face and she fell to the ground. I immediately felt horrible and apologized and was very upset. I didnt mean to do it at all I was just so angry that she blacked my eye. What can I do to not react like that ever again?