You find out it was unfair months later
Most people register an imbalance while it is happening. You register it about six months afterwards, usually as a mood rather than as a thought. Pluto in Libra in the 12th house puts the whole question of fairness where you cannot see it operating.
The Libra colouring is inherited from the period rather than from you, since Pluto crosses a sign over decades and everybody arriving in that window carries it. Your birth time placed it in the 12th house, which is the individual half. It puts the balancing instrument out of view, which is why you accommodate automatically and discover the cost long after the arrangement has hardened.
It happens before any decision is made
It happens underneath any decision you would recognise as one. You adjust to a person's preferences, mood and expectations before choosing anything, and afterwards you would sincerely describe it as having wanted the same thing. That is not dishonesty, it is a process running out of view. The tell is being unable to say what you would have preferred if somebody asked you directly and immediately.
Nothing gets raised while it is small
Because the ledger is invisible to you, nothing gets raised while it is small, and the accumulation eventually surfaces as a withdrawal you cannot explain to the person concerned. From their side it arrived without warning. Write down what you actually wanted after any significant conversation, since the writing is the only way you will see the entries.
What people meet
They meet somebody genuinely easy to be with who has no visible edges and no evident requirements, and a few of them adjust their behaviour accordingly over years. Most are not being exploitative. Say one preference out loud a week, deliberately and about something trivial, since the practice is what makes the larger ones possible later.
Seeing the imbalance in time
What you need is an external record rather than better self-knowledge, which has not worked. A short weekly note about what you gave and what you got makes visible something your internal instrument reports far too late. Keep it for three months and read it as if it described somebody else's arrangement.
The preferences you cannot locate
Asked what you want, you produce an answer that takes the other person into account before you have consulted yourself, and by now you would struggle to say what the unadjusted version would have been. It exists and it is quiet. Notice what you choose when nobody is present, since those are the only uncontaminated data points you have.
You are worn down by company you enjoy
Even with people you like, sustained company costs you in a way that is not proportionate to the pleasure, because you are continuously adjusting to everybody in the room. Solitude is not a preference here, it is recovery. Build it into the week as a fixed requirement rather than taking it when everything else has been accommodated.
Nobody has been told what would be wrong
Your partner has no idea what you would find unacceptable, because you have never stated a limit and have adjusted around every approach to one. From their side there is nothing to avoid. Say one thing you would genuinely not tolerate, calmly and in advance of anything happening, since a boundary described in peacetime is a gift and one discovered in a crisis is an accusation.
Keeping the peace was your job first
You were managing the atmosphere between two people before you were old enough to be asked, and the habit went in so early that it now runs without your noticing it start. It is why family occasions leave you flattened. Sit out one disagreement entirely this year and let it be somebody else's to resolve, or nobody's.
The unpleasant part is done quietly by you
Somebody has to absorb the friction between two colleagues, and it has been you for years, in conversations nobody else knows took place. The team works because of it and no record exists anywhere. Say what happened in one specific instance at your next review, since a function performed invisibly grows steadily and is never once counted.