Is it ok for a married man to start acting like he is single and 21 again?

My husband of 4 years now has started talking to another woman just as a friend he says. But he is trying to hide it. He bought a seperate cell to talk to her on. He is going out to clubs, strip clubs, not coming home, going out and drinking and not coming home until 5 am. And when confronted with all this he thinks its ok and that he doesn't have to explain anything.