After reading your post I felt it in my gut...so I can understand your pain.
I had 2 seperate an opposite thoughts on this. 1) the concept of gas lighting. The term and concept has been kicked around here a couple of times I never really believed in it ...but under the circumstances its worth asking the question.
2) The experiment was to move to a secondary role..... If that's truly the case why do they need to keep you in the loop if you were out of town ...10 hrs away. Now violating your space ..not cool ...but having a party in the general space?
Put another way Have secondaries who were out of town been upset to learn their primary had a party at their home......without notification? Is that an expected right?
This experiment was your idea right?
Could there be an element(s) of passive aggressiveness to this. Be
careful what you wish/ ask for? The party....the email ....moving your clothes. All to highlight your decision?
I guess that's 3 thoughts ...