I am sorry to say, it seems you have taken in so much from the so-called psychologists that you forget reality. Psychologists talk about normal, but normality does not exist in life.
Why would your dad apologise, if he did not mean it? That would be deception. I am afraid, people should mean what they say, at any time, all the time.
You see, you will never know why he left, your mum might know, and that could be her reason for her apology.
The only fault your dad has is not separating the love of his children from that of his wife. Most men see children as extension of their mothers, unfortunately.
Later as you mature in life, you will realise that your dad is entitled to guard his happiness. It is an essential part of his being. Do not blame your brother’s bad behaviour on your dad’s departure. It could still happen if your dad had been around.
Now you are privileged to go through all these rich experiences, I very much hope they will teach you important lessons of life in living your own life in a responsible manner.
I will end with an Indian Proverb, ‘’Do not blame anyone until you have walked six moons in his mocassin.’’
I wish you miracles.💔💔💔