I don't know what kind of person one must be for a significant-other to leave you without explanation and this to be considered normal behavior. I've been let go from one job and they provided me with an explanation; the company lost a lot of clients and 80% of their workforce.
Now I'm the one not following you, so maybe we're just missing each other on this. I don't see the analogy between posting revenge porn and seeking an explanation on a course of self-improvement.
The comparison is not with the explanation but with the action you would take if you don't get an explanation. Yes, it would be nice to have one, yes, it's borderline creepy to retaliate if you don't.
I've only ever had at-will employment so perhaps that example doesn't translate well to your situation - if so, ignore it.
I'm not assuming it is against me, which is why I haven't drawn any conclusions without hearing from these users directly. Again, we are talking about principles and concepts, not my own personal feelings about my situation. This is another benign situation that I am unconcerned about. Assuming I'd like to provide disincentive to discourage unexplained simultaneous movement within the trust-network; what options are there outside an exclusion of those users?
Anybody can exclude anybody they want and they don't need to provide an explanation. Even if you're convinced otherwise - it's impossible to enforce explanations and impossible to retaliate against everyone consistently so the whole discussion is becoming kinda pointless. Do what you think is best but don't be surprised if someone interprets it as petty. Personally I think you'd be hurting your chances of a potential future inclusion if you do this.