Hello!
I'm a lifelong member of the constipation club and I have an anal fissure which reopens from time to time, the specialist who examined me said it was like a scar or something, weakened and easily reruptured.
I have an elongated bowel, so it takes much longer for food to reach its destination, which tends to make it too hard.
My eldest DC has also had the same issues since birth.
OP the daily diet you posted has too much dairy and too many carbs. They're my favourites so I know from personal experimentation (as well as testing things out on my DC) that too much dairy, bread, pasta, rice, crisps and bananas (I don't like them mushy, ugh) will cause really bad blockages.
Movicol two times a day, plus occasionally three times, is what my DC had to have, for years.
It does get better. There are side effects from movicol, but over time the problem clears and any fissures will heal.
I would do what a PP suggested and see your GP, mention the surgery, say that you'd like to try movicol first at a medium to strong dose to begin with, before resorting to surgery.
And please do change that diet. It sounds good but it isn't. More carrot and cucumber sticks, and grapes, these are how I get the DC to improve their diet when we've been a bit lax.