Their previous relationships

According to a survey by the British dating site Illicit Encounters, which involved 2,000 people, around 45 percent of surveyed men admitted to lying to their partners about their past relationships. More specifically, about cheating on their former partners.

The reason for lying is to avoid scaring off a potential new partner. Also, to prevent the other person from creating a negative image in their head. Unfortunately, lying about this is not a good way to start a relationship which should be based on trust and honesty.

See also:10 Cruel Things Men Do to Their Partner, According to Women