Do you apply that to everything in a relationship?
Yes. It isn't an especially controversial or remarkable standard. "All else being equal people can do what they want to, particularly regarding the disposition of their own person, so long as it does not interfere with other people".
Is someone who wants the other partner to stop talking to them also "totally in the right"?
It is a valid preference for them to the have and in they are "totally in the right" in expecting to be left alone if they actively seek privacy. The "right" to have another person unable to speak doesn't follow.
Responding to the inferred intent of your questions I'd like to emphasize the phrase in the grandparent "just choose the BATNA". Thinking through the implications of that you may find that my position isn't quite as objectionable as your first impression suggests. Someone being "in the right" when doing a thing doesn't preclude dumping them the instant they do it and finding someone more suitable. That too is a 'right' (for whatever that is worth).
"All else being equal people can do what they want to, particularly regarding the disposition of their own person, so long as it does not interfere with other people".
Note that you're not actually giving a low-complexity ‘first principle’ from which to derive stuff, but merely hiding complexity away into the word “interfere” -- ‘normal’ humans (who already know what you're saying on some level) will understand (except possibly in borderline cases), but try explaining to an alien or an AI what exactly counts as “interference” and what doesn't.
David is an atheist. He is dating Jane, who is a devout Christian. They have a fairly good relationship, except in the sex department: David thinks that having regular sex is important in a relationship, whereas Jane would like to remain a virgin until marriage due to religious reasons. Before they became a couple, David assumed that not having sex was something that he could tolerate, since he liked Jane very much, and was really eager to be with her. However, as months go by, David has become increasingly frustrated with the lack of physical intimacy, and is beginning to consider breaking up with Jane, even though he is still very fond of her.
What would you advise David to do? Given my experience, I think the most common response would be to advise David to leave Jane. Some people might even say that David shouldn't have started the relationship with Jane in the first place, since he has known all along that she intends to remain a virgin until marriage. They say that, if he really loves her and respects her religious beliefs, he should not ask her to have sex before marriage. Instead, he should break up with her so that they may both go on to look for more suitable partners.
Why is it that nobody says that Jane shouldn't have started the relationship with David in the first place, since she has known all along that he thinks that sexual compatibility/activity is very important in a relationship? Why is that nobody says that if she really loves him and respects his values, she should not make him abstain, and should instead engage in sex with him? Why do her religious beliefs render her position more privileged?
Perhaps the response would be this: Well, the criticism is mostly directed at David because he is the one who went into the relationship with unrealistic views of what he can or cannot do. Besides, since Jane lay out the terms clearly before they became a couple, then she could hardly be faulted.
That is a reasonable response. But imagine if the situation were reversed: What if, while they were still discussing whether to commit to each other, David lay out the terms that Jane would be expected to have sex regularly with him? Even if she agreed, chances are that people would say that he should have respected her religious convictions. Those who criticise David might point out that perhaps Jane was very reluctant when agreeing to it, but thought that it was something on which she could compromise, and that David should not have put her in such a difficult position in the first place. Well, then, perhaps David was very reluctant when agreeing to not have sex as well, but thought that it was something on which he could compromise, and Jane should not have put him in such a difficult position in the first place.
The emotional harm done to Jane by making her engage in pre-marital sexual activity could be as severe as the emotional harm done to David by making him agree to abstain from pre-marital sexual activity, and yet few people acknowledge it, at least in my experience. Or maybe many people do acknowledge it, but nevertheless there are few of them who would admit it openly and defend David. Why is wanting sex worse than not wanting sex?
What is it about being religious that gives one the more privileged position in love?