Am I overreacting?

So I got a message from this guy this morning saying my bf is fooling around with me a girl at his work. So I asked him about it and he denied it. I don't know if I believe him because a year ago I caught him in a lie texting another girl and I asked him about it and he said it was his mom. I'm not saying that I believe that guy. But it's his* actions after we got into an argument. He was and probably still is sleeping like are you kidding me??

Wouldn't you try and prove that you did not fool around? I mean yeah he did call her about it. But its the fact that he is sleeping like it's ok. I know guys have girls as friends and I'm cool with that but it seems like every time a new girl starts working at his job he always gets her number.