Why do MEN love to lie? Is it that hard to tell the truth?

So I met this HOT guy back in novemeber and ever since then til March I have been seeing him off and on. we were never in a real relationship but we would act like we were in one cause we liked each other ALOT. He would asure me that most days hes busy and has no time for girls and Im the only girl hes seeing.He would usually come see me by his schedule since he has a car. through the 4 months of knowing him I seen him at least 10 times.We would see movies, play pool, go bowling, or just sit in his car and talk for hrs. i admit we had sex only twice but our small relationship was more then that for sure. the last time i saw him was march 31st and i hadnt hear from him since....i decided to look him up on facebook and found out he recently met someone and is in a "RELATIONSHIP" now with sumone. Why didnt he tell him? how come he hasnt called me? even just to tell me he has sumone now. i wouldnt be mad cause at least hes being honest and I would have been okay being just friends. WHY DO MEN LIE BY NOT SAYING ANYTHING??