I’ll add to the list: doctor-patient, lawyer-client, judge-lawyer, judge-litigant, social worker-charge, police-detainee, prison guard-prisoner, etc., even in contexts where there is no actual coercion. There is more to relationship ethics than consent. You have to consider the ethics in the context of the other relationships between the parties. Lawyers engaging in relationships with their clients is in fact an ethical violation, regardless of consent, because of the possibility of or appearance of abusing the lawyer-client relationship. Relationships necessarily also affect third parties (other partners, coworkers, etc.) Those effects must be considered too. People owe each other (not just partners, but third parties) more than just not committing rape.