What is the WORST thing someone could do in a relationship?

Everyone has certain boundaries in relationships and different ideas of what actions they consider the worst…
So, in your opinion, what is the WORST thing someone could do in a relationship?

My answer: I would have to say cheating and lying are equally the worst things someone could do in a relationship. Even worse, LYING about CHEATING is the worst thing you can do in a relationship.
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And abuse, physical, emotional, verbal…
What is the WORST thing someone could do in a relationship?
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