Are psychics the new detectives? – Lifestyle – DNA.
Apparently Tarot Readers in India are being asked to investigate whether their client’s significant other is cheating on them! Unfortunately the article is short on technical data like which spread to use, etc. Obviously they don’t want to give away their trade secrets. 
Sol Ascendans - The Website of Alex Sumner 
That’s a question in need of careful handling and almost certainly, re-phrasing. If they suspected they were being cheated on, their suspicion would probably be reflected in almost any general spread. If their suspicions had any basis in fact, a single card spread or a counting/odds spread would give a weighting, with comments, watching out for the Moon card, Lovers upright or reversed, Devil, 3, 7 Swords, 9 and 10 Swords. No need for a single spread prescription.