Student or Learner
Must friend: a best friend, a member of your inner circle, a person you count on when something big happens in your life
Do You Have These Friends? | Psychology Today
From the given context, do must friend and true friend have the same meaning, please?
In fact, I've never seen it before. Ever.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
I find their decision to make all the descriptions of friends rhyme rather odd. It has led to very unlikely collocations with "friend" - Must, Trust, Rust and Just. I think they were very desperate to make them rhyme, and they probably started with "just". I don't think these terms will catch on.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.