Hi,
it's not such a big deal if your boyfriend lied to you for some reason...give him a second cheance...sometimes in life it's better to lie than to tell the truth. He will appreceate you more if you'll not say almost everytime that he is a lier, but will let him to get back to you...In fact I don't know what kind of lie was...if he went out with another girl but told you that he worked late - this is serious.