Is withholding affection/sex a form of abuse in a relationship?

I've had a friend trying to convince me that someone withholding affection/sex in a relationship is a form of abuse. I'm guessing they are looking at it as if you are knowingly withholding these things to prove a point or to get what a person wants. However, calling it abuse seems a little much. What are your thoughts?
Is withholding affection/sex a form of abuse in a relationship?
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