just make it realistic mate, dont chat rubbish and make a massive lie up make it real. But whatever you do dont tell the truth, i did and it....well didnt go down well :) good luck
It depends what sort of lie it was like just a little or big. You should talk it over and see what the reason for lying was if he still or you feel that he's lying maybe you should find you another...
I think that it is because they are worried that you might break up with you and some times it is because they don't want you to be worried. Sometimes they just are a holes. :)
Your boyfriend would lie to you about questions such as...hes not cheating on you, he still finds you attractive, he loves you etc. It depends on what there is to lie about.