Once a hitter, always a hitter?

I have slapped her back (always and only in retaliation) but six months ago she was screaming at me (again for something quite trivial) and she went to hit me but I grabbed her arm to stop her and twisted it.

I broke her wrist in three places and when we went to A & E I was going to tell the truth as to how it happened but she lied to them and the doctors and nurses knew it. I have never felt so awful in my life.

I cannot justify what I did in any way and I blame myself completely. I hated myself every time she had to lie to friends, her mother and colleagues just to 'protect' me. I wanted her to tell people the truth despite the fact that no-one would ever want to know me again. I hated myself every time I looked at the plaster on her arm. I hated myself for the physical and mental pain she suffered.

She now tiptoes around me, which I hate, and is very selective about what she says to me, despite us having talked this through 1,000 times. We are very much in love but she doesn't bring things up that are likely to cause me to raise my voice.

My problem is that I want to go and see a professional group for men who abuse their partners and ensure that I get proper advice and attention so that this never ever happens again.