How do you tell if your bf is lying to you?

It takes a while, for a man to accept that he has lied to you and to admit it. The only way, is easing it out of him, and telling him you need to know the truth or the relationship may not last. Also, if you are certain, try telling him you will leave him unless he admits it. But if all else fails, and you are still certain, look for body language. Sit in front of your partner, and simply ask him the question. Eg, "Are you lieing to me?" or, "Have you cheated on me?" out right. If he does fidgety movements, even like a hand movement or a shaking leg it is 99.9 % chance he is lieing. As well as that, there are also unstoppable small body movements, like a pupil contracting or the eye twitching. Good luck ! If you think he is lying to you about lying, then how will you know when he is telling the truth about telling the truth?