@Cantwait4summer94 I can see why these comments are hurting you because you're feeling dreadful and guilty but I do also think you need to listen and take them on board.
There seems to be some perception about abuse and harm in childhood that it's perpetrated by 'bad' people and not parents who love their children, maybe because that's easier to believe than the alternative.
It's not true though. People aren't good or bad, they're complex. You could be a lovely person but if you don't have control of your emotions and your actions, you could still cause emotional and physical harm to your child.
I'm sure your child is fine but equally they may well always remember the day that mummy lost control. Hopefully this will be because it never happened again.
The impacts on children isn't just about the 'smack'. It's the fear it will happen again, the worry that mum isn't ok and the risk of that secure base being a bit wobbly.
Can I trust this, am I ok, am I safe. Is mum/dad/whoever still in charge and in control?
I know you know it's wrong but actually losing your temper and repeatedly hitting your child is abusive. So accept that and strive to be different.
What are you doing to reduce your stress levels and make sure it doesn't happen again?
What is your plan for the next time he or his sister are driving you completely potty because all kids do at some point?
How will you respond?