Long term boyfriend is struggling with conflicting thoughts and bringing me along with it. Is he a cheater?

I have been in a relationship with this guy for almost 8 years now. We are both 25 years old so we've met at a young age. College years were the hardest, especially for him. He wanted to know what other girls were like....so we've tried an open relationship, didn't work so then tried to break up....didn't work. We just kept coming back together. But we have dated other people on the times that were allowed, he had slept with several girls on our off times. I was hurt by it but I knew it was for our best interest besides I did the same and dated a few guys. We ended up getting back together. I thought he knew for sure I was the one for him. We had been living together for 3 years now and just recently I have noticed something"off" about him. He was more curt, angry, I didn't know how to help him. He didn't seem happy. He has family in NY and we are in Philly. The last times he has gone up there he had hung out with some childhood friends of his (most of his friends are females). I didn't know about this until he would come back and I manage to find out. I look at their myspace and they came off trashy and slutty. I confronted him, that I felt uncomfortable that he had spent time with them without me having to met them. He apologized and told me the next time he goes up there I will get to meet them. Well just recently he wanted to go to NY, and with our history, I asked if I could come. He said he wanted to be alone. So I let him go. All night I was tossing and turning, so I decided to go on his email (yes bad on my part) and noticed he had been in contact with this girl in NY. He lied to me and said he hasn't spoken to her and hadn't plan on it. These were flirtatious emails. I know that in the past I have cornered him and yelled, screamed, cried because I didn't know these girls and yet have met them. I know he probably was scared I would start that behavior up again if he had told me he was to hang out with this girl. I called him at 6 in the morning in tears, hyperventilating....fortunately he was at his families house that night in ny and no where else. He starts crying as well. Says he is a bad person, he has been ridden with guilt, and was planning on breaking up with me that day because I deserve better and that he is a bad boyfriend because this entire month he left me in a lie. He says this whole month he hasn't felt himself, he hasn't been patient, compionate or healthy and whenever he bickered he wanted to run away. But that he loved me with all his heart and feels with time apart may help him resolve underlying issues of his. I ended up talking to the girl over the phone and so she claims that he is a family friend of hers, it would be like if they slept together, that he speaks of me and that she has always wanted to meet me but found it odd that he never wanted our worlds to collide. I spoke to my guy about this...he said that we are very different people, come from different backgrounds and is not sure if I would feel comfortable around her. She is a supermodel, travels the world and tries every drug possible and I am this girl next door type. She actually had me talk to a guy friend of hers...he said she is just extremely flirtatious, she is actually engaged to getting married and has a daughter. She is extremely blunt and talks dirty to everyone. So they both claim they are just friends. Nothing would have ever happened. But he did commented that it was in his thoughts that he wanted to sleep with her (although she is convincing enough to say that would never happen) but he feels ashamed of these thoughts and never acted on them but they did come across his brain.He promised that next time I will get to meet her when he will go up there. But overall, he lied to me and feels guilty about it....feels guilty enough to say we need to be apart. Well the other day he comes over, says he wants a future with me but for now he needs to be alone. He knows it would be unfulfillable to sleep with other women even though he desires it. He wishes he could have me and that. But won't do that to me. I can tell he loves me but he is conflicted. He wants to be alone for awhile, to reflect and wants me to know that if I wanted him back he would come back instantly but I know for his best interest thats probably not the best move. He doesn't want me to wait for him to get better and that I can see other people. But I know I can move on, anyone can...there are more than one shiny fish in the sea. He wants us together, just not now unless I really want that. What should I do? Is he really that bad if he never actually done anything but just this lie which he is tormenting himself over currently. Now I don't know what I want, or should want. Help. Should I forgive his behavior? Should I make him suck it up and be in a relationship with me and possibly work on this communication and honesty (he says he doesn't want to lie to me again). Ahh, help.