Cheat is a blurred and emotional term like love.

To him, basking in the glow of a platonic relationship may be OK,

to her, a cheat.

Phone sex, or cyber sex may or may not be, depending on viewpoint.

Sex in an open relationship may not be (at a stretch).

Morals are the limits you place on yourself, and when you cross the line,

you've done a bad thing.

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Calm, quiet, smooth, devastating