Assume that two parties have a certain level of high commitment in a romantic alliance. Now suppose that one party suddenly schemes to launch the Placeholder Doctrine...
The Placeholder Doctrine (a term I've coined) is a controversial strategy used in the romantic relationship game where one of the two parties has already secretly and privately determined that their romantic ally will 80-90% be abandoned at some point. However, rather than openly declare this to the ally so they can make preparations and everyone can move ahead... the user of the Doctrine takes covert action to use their radar to find a replacement ally while maintaining the existing alliance.
The person using the Placeholder Doctrine does so because they don't want to be without allies at any time (they enjoy the benefits of the alliance; largely how things appear formally, the existing financial arrangements that are beneficial and perhaps the physical entertainment). The other ally thinks they are still in the alliance but really they are being "used" at this point; the other ally is simply treating them as "the best they've got for now."
The user of the Doctrine is "safe" in the sense that in the worst case scenario, they find no one better and they keep their remaining ally and won't end up by themselves. However, they've massively increased their own probability of finding a better ally because they will be making tons of moves behind their previous ally's back to send the feelers out.
During this period, it is usually the case that the dynamics of the formally existing alliance will deteriorate unless the user of the Doctrine is particularly skilled at the art of deception. Since the user of the Doctrine has made a secret determination to switch allies (just a question of When the opportunity arises); if they are especially callous they will sometimes treat the other "ally" with distance, increasing contempt, and a bit of passive aggressiveness while going through the motions of the existing alliance.
Often, the end result is that the user of the Doctrine suddenly ditches their allies, declares their allegiance to a new romantic ally, and the previous ally is completely shocked at the sudden betrayal and left heartbroken. The user of the Doctrine will then tell them, usually somewhat coldly, "Well both of us knew this wasn't going to last (except I decided a long time ago without saying anything and I've made my preparations while you didn't know better and continued to provide me with the fruit of the existing alliance)."
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On the one hand, it sounds unethical when phrased like in the above but on the other hand... relationships are about choices, personal choices. So who's to judge?
Is it ethical? Discuss and explain.