Conventional descriptions of Activity describe a relationship that "over-energises" each partner until they burn out. The essence of this seems to be a positive feedback loop.

With other ISFps, I've found that we often wind up in very energising creative-Fe competitions. At the moment, this is manifesting for me as increasing attempts to get an ISFp I know to laugh, intensified by my own amusement at trying to get reactions out of her. In the past it's manifested as general trading of trivia and prods to get reactions out of the other, in a general Alpha Fe kind of an atmosphere.

OTOH Activity has usually been one where I can talk for hours and come away smiling, albeit without the emotionally rejuvenating effect of duality. I think my interactions with my Identicals are far more "activating" than with my Activators.