It is always better to tell the truth; it makes you a trustworthy person. I agree that there is no justification for lying. When you find out that you have been lied to, it just makes you lose trust in the person and will always make you think twice before believing the person again. I don't think it will kill you to tell them you were looking out for a better opportunity. I believe you should have some leave days to yourself, so they should allow your absences for a couple of days.