The two halves have the same weather
Because your Mercury reads in Pisces and applies it to the 12th house, the two halves have the same weather. The sign already dissolves outlines and the house is already the department of what runs underneath, so there is nothing here to balance anything else.
Traditional astrology counts Mercury both weakened and fallen in this sign, on the grounds that it cannot do what Mercury usually does. Our reading is that it does something else entirely: not classification but absorption, and the results are unprovable and frequently right.
What the tradition is actually pointing at
The complaint against this placement is real: the specifics go, the reasoning cannot be reconstructed, the account of how you knew is unavailable. That is a genuine cost rather than a slander. Handle it structurally instead of arguing with it — write things down, confirm arrangements, keep one person nearby who deals in dates — and the objection loses most of its force.
You know things you cannot source
Information reaches you without a route: what is wrong in a situation, what somebody is not saying, how a thing is going to go. You dismiss most of it because there is no evidence to offer. Keep a private record of the first impression against the eventual outcome for a year. The record is the only thing that will settle the argument you keep having with yourself about this.
The boundary is the entire practice
With no outline on either half, you take in whatever is present — a mood, a crowd, another person's difficult month — and cannot say afterwards which of it was yours. That is the one thing worth working on here and everything else improves as a consequence. Name it rather than resisting it: this is mine, this arrived with somebody. Naming works and resisting does not.
Solitude is not optional in this arrangement
Long stretches alone are the condition under which anything gets processed, and without them the accumulation simply continues. People read the need as antisocial and it is closer to a physical requirement. Schedule it in advance, before you are depleted, because in this position the recognition that you needed it arrives some weeks after the point at which taking it would have worked.
The sensitivity needs a channel or it turns inward
Undirected, this receptiveness becomes an internal weather system that runs continuously whether or not anybody is served by it. Directed, it is a genuine vocation: writing, care, anything requiring somebody to know what is going on before it has been stated. Give it a channel with an output attached. That single decision is the difference between a gift and a burden, and nothing else in this arrangement substitutes for it.
You dissolve into whoever you are with
In closeness the boundary between you and the other person disappears rapidly and pleasantly, and it feels exactly like the thing you were looking for until you cannot locate your own preferences. Keep one part of your life the relationship does not enter, chosen at the beginning while it is easy. That is what makes merging survivable rather than something you eventually have to escape.
You come back from company depleted
An entirely pleasant evening can leave you flattened, because the load here is what you took in rather than what you did. There is nothing to fix about the evening. Build an emptying step into the way home — a walk, twenty minutes of nothing, no further input — and treat it as part of the outing rather than as recovery from it.
You did the feeling for everybody
In a household where something was not being processed, you did the feeling on everybody's behalf — without anybody asking, without it ever being noticed, and long before you were old enough to decline. That role was assigned early and has never once been reviewed. Notice when you are still doing it now, in adult life, for people who are perfectly capable of handling their own material and would be surprised to learn you had taken it on.