Is my bf cheating? What should I do?

So I need your guys opinions because I really don't know what to think, or if I am overreacting. I have been with my boyfriend for 7 years, we have 2 kids together and have had our major ups and downs. We work in the casino industry and I have had multiple girls come up and tell me they have done stuff with my boyfriend and he always denies it. I have always given him the benefit of the doubt until recently. When I was pregnant with our second child, I had major complications, I was sent to the hospital from work and I couldn't get a hold of him. Come to fin out, he met up with his ex and was with her for 3 hours talking, when I was upset about it, he said he wouldn't do it again, but continued to do it anyways until she moved. It has been two years now and it is starting all over again with a different girl. This girl is a girl that like him in high school, and is going through a seperation with her husband. They started talking on Facebook, and all he did was completely trash me and said how we were just roommates. The girl called me and told me about it and said she though I should know that although they are not romantically involved, they are seeing where things go. She said there isn a problem and he's not cheating because they haven't slept with each other, I think otherwise. So when I confronted him about the phone conversation, he denied even talking to her and said he was going to fix it. Apparently she told him I was lying, and he believed her. Then he lost his phone and I left mine at the house because of the kids, when I got home from work, there were a bunch of messages about hanging out and everything else from this girl. I still got the messages the next day and continued to show him them. They were as bad as she can't keep her heart waiting and he beds to decide. He asked her about them and she denied them again, even though he seen the messages himself. He said that he wasn't goin to be friends with her anymore. I went to work, and they continued to have long Facebook conversations with me and she was taking pictures of the conversation and sending them to my phone in a text. When I got home I showed them to him and he denied them again. I asked him to see the conversation then and he said he deleted it. Only to find out that she is meetin up with him today at his work for lunch at 3. And now he is mad at me because I say he's cheating and he said it's just a friend and I need to but out. I really don't know what to think and my family keeps saying that he's cheating and move on, but I would like some other peoples opinion on it, and maybe even some advise as how to handle it.