Whats the purpose of a side piece?

Hey y'all I've always wondered what's the purpose of being in a relationship if your have a side piece? The moment the person's husband/wife starts acting up they run to the side piece. Now it's obvious that they are more in love with the side piece than the main person there with but why not just be with the side piece in the first place. Cause all they do is get mad run to them and start snitching
Whats the purpose of a side piece?
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