Hiding something

My boyfriend just started hanging and texting one of his old friends Jeffrey. They talked on the phone. And didn't tell me their conversation (he usually tells me everything) he said it's not important, simple conversation like grown men, it had nothing to do with you, no need to worry. So I got pissed, saying are you cheating on me, why can't you tell me, now you are making it seem like you are hiding something. And to this day won't tell me what it was.. Am I overreacting...