Who's worse? The Cheater or the Side Piece (assuming the Side Piece knows they are helping the Cheater cheat)?

Both are bad, but which is worse?
Cheater
The Side Piece (assuming they know)
Select gender and age to cast your vote:
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+1 y
I didn't specifically say whether any party was of a certain sex. It is a generalized question for the topic.

For those saying "the girl cheated on needs to improve her sex game" what if it was a male who was cheated on? What's your advice then?
Who's worse? The Cheater or the Side Piece (assuming the Side Piece knows they are helping the Cheater cheat)?
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