What to do about lying boyfriend? please help..?

I had been with my boyfriend for 6 years but within the last year or so I had caught him lying a couple times but he swore to never do it again and we barely spent anytime together b/c he was always going to bars after work and I had class.. last night he had went to a guy friends bday party at a bar and called to ask if I was coming to his house afterwards and I said no I have to much homework to do and I wasn't coming to his house at 2am... Later on I had called him over and over and he wouldn't answer then he shut off his phone. I was gonna stop by his house b/c I finished my classwork and at 4am he still wasn't home and I saw his vehicle at his work.. he finally called and said his phone died and hewent to mcdonalds then home... when I knew that he was in the parking lot... I asked him a few times if that was where he really was before I told him I saw his car at work. He then said "oh yeah, I was smoking in the parking lot with Sarah" it's not lying and i'm overreacting first of all he knows I don't like when he smokes stupidly and second of all I told him I didn't want him hanging out with her alone b/c thats what he had lied about before and says there just friends (he works with her)... I haven't picked up any of his calls b/c he said some pretty vulgar stuff to me after I confronted him about lying. Should I just walk away from this relationship and never talk to him again.. I just feel like it would be wrong b/c we were together for so long but I just don't think he's gonna change back to the way he use to be...