Damned if I know. The Napoleon complex I have an easy answer to; you can't pursue that one without violating the ZAP, so clearly it is not OK. Ditto the romantic breakups - those are strictly internal choices, which cannot be physically pursued by the one party without initiating aggression against the other. I do think that romantic relations would become a lot healthier without the pressures and foolishness of today's world, but that might be wishful thinking - men and women will probably find new and exciting ways to screw up each other's lives.
What I think you're missing here is the *directed* nature of shunning. A romantic breakup does not in most circumstances have as its *object* driving the object of your former affections nuts. Shunning DOES, and I think that counts for something. But, hell, I am a practical sort, I'll leave the theory to the people what cares. For me at least, shunning appears to be a weapon that needs to be used with attention to the moral implications. Others can make whatever choices seem right to them; I can't stop you anyway, and wouldn't care to try if I could.
It occurs to me, Sunni, thinking upon some things L Neil has put in his books, and some discussions I've had with him on other subjects, that I *do* have an answer of sorts for your question. Any time you inflict pain, I think there probably IS a moral debt incurred. Like the alien in "Forge" who caught himself on somebody else's balcony to save his life, and had to trespass as part of that emergency, there may be a vital and over-riding reason for you to do it. That does not of itself erase the debt, though. I am dubious myself just how far one can take that concept, for it has lots of implications that would need exploring.
My point is that you can establish a moral calculus - killing someone is wrong, but if they initiated aggression against you and you did it in self defence, then his greater moral debt cancels yours. Similar arguments could be applied to both the Napoleon example and the romantic breakup I should think. But that may be stretching things beyond the breaking point, I dunno. Never thought about it in those terms before; I *said* when we started this whole discussion that I was wondering how the ZAP applied to shunning. I'm a simple man, and I like to keep things simple - the ZAP is simple, therefore I like to use it when I can. QED.