To find out more about identifying a liar, see our page on How To Detect Lying to learn how to question and dig deeper when you suspect he's lying to you. He used to be loyal, but now he cheats. This is one of the reasons men cheat: New purchases such as new clothing, new shoes. He has started to show interest in new topics, activities, or sports that he was not previously interested in. The list of dating applications and websites is seemingly endless these days. But unless he can show you that picture, I would go ahead and show him your middle finger and perhaps the door. Is a Twitter or Facebook user — The data is in. Closing thoughts We hope you've found this article useful. Secretive Behavior When your boyfriend has a secret, he will try to hide it from you. Has picked up a new language — Come on, how else do you expect him to be able to communicate with his new exotic girlfrienda? Things got too serious too fast — Did he ask you to be his girlfriend on your first date? Out of guilt or fear of being caught, he may suddenly stop talking about her when he starts having an affair. Often this can be a good thing, if you know what it is and what's going on; for example he may have overcome a period of depression. Has selectively updated his dating profile — Perhaps you two met on a dating site.