No, "everyone" does not lie about sex because "everyone" does not have a need to lie about it. I'm married, in a loving, monogamous relationship with my wife. I don't discuss our sexuality with friends, family or co-workers. If someone were to ask me about it I would politely, or perhaps not-so-politely, inform them that it was none of their business. Therefore, I have no reason or desire to lie about it.
People who betray the person to whom they are supposed to be most loyal in life, their spouse, lie about sex. Sitting Presidents attempting to deny justice to citizens in civil cases lie about sex. Congressional weenie-waggers, who when caught redhanded try to save their own ass by shifting blame to someone else, lie about sex. That's not everyone.
And comparing the lies of Clinton and Weiner to two twentysomethings sitting in a bar telling exaggerated stories about their sexual conquests, or someone overpraising their lover's talents to boost their ego, is not the same thing either. The former have a seedier, more malicious intent and are in no way excused by the latter, more benign examples.