One-Sided Relationship
The same as one-sided love, though in this sense is a generalized term. Here, the interests of the one party are put to a much higher priority than the other. Feelings are unrequited, certain needs go unmet, opposing words are not or cannot be conveyed to the other party, and there is an apparent or explicit lack of importance in the self placed upon by that other party.
Person 1: Why is Frank so miserable when he's with those other friends of his?

Person 2: It's a one-sided relationship, man. They treat him like a background character.