Snapchat cheating?? Help!!

I found out yesterday my boyfriend of 4 years has a 2nd snapchat account to send dirty messages and pictures to women he doesn't know, and they do the same back to him! The account isn't in him name and I have found things in the past on his main snapchat account which raised my suspicions. The last time he claimed his account was hacked... what an idiot I am for believing that! He's been doing it on and off for the whole 4 years we have been together. When I confronted him he said he couldn't help himself and he doesn't know how to stop it. He says he enjoys it because it's anonymous and he doesn't know the women. He also said it might turn him on if I did it to other men but I don't know if he was saying that to get out of trouble. What should I do? Is this cheating?