I am guessing Saku is stuck in a sexual relationship with the professor because he is a graduate student writing his paper and wants it publish (or some kinda scholarship/academic reason). He also prob got traumatize from past relationship where ppl were only using him for sexual gratification or to test if they were gay or not cuz he looks pretty.
qualia under the snow did this trope much better, i dont like when one character puts the other on a pedestal and never dates anyone else themselves, not even try, while the other is sleeping around
it's an unbalanced dynamic