He may not be physically cheating, he might be only talking to people and having "online sex" or "phone sex" which I think is up to each person to decide if it's cheating or not.
But I would not snoop around, I would like Tiggy said wait till he slips up because everyone at one point will slip up.
If you have doubts that he is cheating then your probably right, sit back and wait and see where he slips up as at some stage he will.
If it were me, I would make copies of the things you have seen, show it to him and see what his reaction is. I myself would be leary of any of it. It is ultimately up to you as to how you would like to handle any of it, but if it were me, I would find out how long it has been going on, why it has been going on and then make my decision based on all of that.
Since he's accustomed to lying, he's going to deny, and deny, and deny.
And, even if you get documented proof that he's cheating, I suspect that he'll try to explain it away and continue to deny.
Only thing is... right now, you don't know what to do because you're conflicted. So, give yourself enough of "wait and see" time to decide "if," and how long, you're willing to tolerate all of this... and, when you reach that "last straw," you'll know what to do.
I have seen some of his messages from myspace how he speaks to these young girls, and have spoken to them and they tell me how they talk and what he thinks. i can't hear the conversation cause when he sees me coming or hears noises he hangs up quick and tells me a big lie. i know the true will come out but i don't want to be the stupid one getting played and allow him to keep hurting me. once he left for a whole week and when he came back he gave me this lie that up to this day i do not believe
Can you give more details about what you have caught him in? Like do you hear his telephone conversations? Do you see his messages on myspace? There has to be some real evidence for you to walk out on your marriage. I always think that the truth will come out in time and usually your gut instincts are correct. I would wait it out and see what unfolds. Most likely he is if you are suspecting it.