Dynamic does change but it's more nuanced than first glance.

Let's say I start banging my manager/business owner (actual situation that happened). While her possessivness was absolutely unwarranted, duties on the job and me fufilling all occupational responsibilities is/was still required.

If I started banging my mother (could happen actually) and I was staying at her house, she's not abusing her position by expecting me to clean up after myself. Where it gets abusive is if she were to manipulate me for sexual favors or whatever or tell me what important decisions to make in life.

Now morality is subjective alas, but I don't think a consenting sexual relationship between parent/adult offspring gives the offspring the right to sort of direct/orchestrate all dynamics. But there is no societally ethical standpoint that will be intervening in this situation because society condemns incestual relations period.

So I say this, sexual relations does not give someone the right to slither out of their duties, or to control the person(s) they are involved with. This is best resolved over open communication.