He says he cheated but is it true?

Ohkay 3 nights ago me my boyfriend my bestfriend and her boyfriend where getting drunk at my place and stuff i was wasted but remember everything he was going through my phone nd he say that i was talking to my olddd guy friend from school like a close friend i said mwah to him nd my boyfriend saw it he came to me showing me it and i was just like forget it cause i was drunk then like 5 to 10 min later he comes to room where i was laying down at and said "oh and by the way i cheated on you with the girl i slept with before a month and a half ago" and i flipped out on him .... he told me that it was the day they called him into work for one of his coworkers just for half the shift nd after work he went to her place but a month and a half ago on that day i remeber him coming home to me and we just hung out at home. and went to my moms house. i asked how he got her number again and how she got his and he said i have friends numbers they gave me it but when i go to his "turned off, no service phone" all his calls in call logs are companys and his family and me and two guy friends and those two guy friends are also in his contacts theres and thts all friends numbers he got and when i acted like my boyfriedn texting his friends they had no clue what he was talking about.