1. Sometimes there is another explanation for a person losing 10Ib, working late and losing interest in sex. I just don't know it.

2. You need proof, but cheats guard their mobile phones with their lives and never get itemised bills. If their phone's inbox is clean, look for separate “saved message” folders cunningly titled “extras” or “new account”. PhoneFile PRO Special Edition, £59.95 from www.smartcardfocus.com can recover accidentally or deliberately deleted text messages from your partner's phone.

3. You can track internet usage by installing eNetRespect; £75 (www.nethim.com/products.html ) on their laptop. It monitors online activity and sends an activity report to your e-mail address.

4. If you go looking for dirt, don't be surprised when you find it. James Myers, of Metropolitan Investigations, (www.metropolitaninvestigations.co.uk ) says that “by the time a person hires a private detective they know their partner is having an affair, they just need to prove it”. Surveillance costs £40 an hour and the average spend is £500-£1,500.

5. Why do men cheat? M. Gary Neuman, the author of Why Men Stray and What You Can Do to Prevent It, says that only 8 per cent of men blame sexual dissatisfaction at home, whereas 48 per cent say that they feel under-appreciated by their wife.

6. Mind you, men are more likely than women to justify their extramarital sex and they experience less guilt when they engage in it.

7. Why do women cheat? General dissatisfaction with their marriage and revenge against a cheating husband. But women whose husbands have affairs are more willing to forgive their partner than men whose wives have affairs.

8. Men and women react differently to spousal infidelity. Psychologist David Buss says men tend to focus more heavily on the sexual aspects; women on the emotional aspects.

9. Although extramarital sex is the most cited cause of divorce cross-culturally, over the course of a marriage, studies show 30-60 per cent of men and 20-50 per cent of women will have an affair.

10. Is reconciliation an option? Only if your partner is willing to end the affair immediately. If both of you can commit yourselves to improving your relationship, and you can diffuse your anger enough not to keep hauling your partner over the coals, counselling may help. Contact the Tavistock Centre (www.tccr.org.uk ) or Relate (www.relate.org.uk ).

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