Are his online messages evidence of his cheating?

I have recently discovered that my boyfriend over a year is cheating on me. He swears up and down that nothing is going on and doesn’t understand what I’m so upset up.

He has always been pretty secretive about his cell phone and myspace account but has really gotten bad about it in the last couple of months. I found flirtatious text messages on his phone a while back that he had sent to another girl. When I confronted him about it he said that she was just an old friend of his. The messages, however, were more than just friendly messages. Another thing that made me so supicious in that instance was that I have met all of his “good” friends and I have never heard him talk to any of them they way he was to her. The messages were comparable to stuff he sent me when we first started dating.

Then more recently, I got onto his myspace account to find messages sent back and forth between him and another girl. He was talking about going out to a local bar and meeting up with her. He told her his was single, asked her to have Valentine’s with him, and discussed going back to her place. Saturday night he told me he was meeting up with a male friend of his to go shoot pool but I couldn’t go because it was a guys night. (Note: In the past he always insisted on me going out with him and the guys.) Later that evening, after he left, I found messages that he would be available that night and asking to see her. I printed the messages so he couldn’t delete and deny them but yet he still swears up and down that nothing was going on. For me it is pretty obvious that it is. He says he was just “talking” and that he never did anything with her and never intended to but I think it is pretty clear he’s lying.

Do you think that the messages I found are evidence that he was cheating and I should give him the butt?