A girl who is going to help you with your study and all of your trouble does not exist.
A girl who told him that he was good-looking does not exist.
The reasons (because-clauses) are my guesses, so they can be imaginary.
So this got me to think: Does this kind of structure have anything to do with a second or third conditional structure or are they just normal past tense and future tense?
Are parts in bold correct?