Betrayal of the altruist

Betray, according to an online dictionary, means

To give aid or information to an enemy of; commit treason against: betray one's country.
To deliver into the hands of an enemy in violation of a trust or allegiance: betrayed Christ to the Romans.
To be false or disloyal to: betrayed their cause; betray one's better nature.
To divulge in a breach of confidence: betray a secret.
To make known unintentionally: Her hollow laugh betrayed her contempt for the idea.
To reveal against one's desire or will.
To lead astray; deceive. See Synonyms at deceive.

I wonder, however, if there is not another meaning of betray, one which refers to a situation in which one sacrifices for another, in the sense of helping them and doing them favors, and that person responds by performing seemingly senseless acts that hurt the altruist and/or her kin.

Altruism always leaves one open to betrayal. In fact, social interactions of any sort probably leave us open to betrayal.

Once, long ago, I remember my father telling me about a good Samaritan who stopped to help an accident victim and ended up being sued by the accident victim. While I do not remember the reason for the lawsuit, or how it all played out, what I do remember is my parents saying that it would have the effect of discouraging altruism. This, it has seemingly done. This act was a betrayal of the altruist.

I read on the internet that betrayal is one of the words least used in the English language. Surely, given the events of our time, it is not because betrayals do not occur. Perhaps it is because such acts are so commonplace.

If you once let a person betray you, you are naive, but if that person betrays you twice, you are a fool.