Unless you are in a fault based state does it really matter if he is cheating. You know in your gut what is going on.

If you have to know I would hire a PI. That would be the safest and easiet way to go. PI's don't usually make mistakes and you would have the info you need. I can understand wanting to know for sure and it would help you make the decisions that need to be made.

I think few members here have hired a PI before.. Anyway, if it is related to computers, like emails, etc.. get a keylogger..

If it is related to cell phone tracking, get SIM card reader (make sure the cell phone model is compatible).

Get a digital voice recorder with a "voice activation" switch. And preferably an amplifying microphone. The recorders are about the size of a pack of gum, and the microphone is about the size of a pea. If not voice activated, most models will still recored for hours. Should be easy to hide. Check Radioshack locally. There's also a wonderful camera store called Supercircuits that has some really cool surveillance shit. Finally, check Chinavasion, they have some hidden cameras (Like in pens and watches and stuff) for very affordable prices. (Like $30-50) I'm going to pick up a couple just to have for whatever I may need them for in the future.
Good luck.

All good advice, iamawarrior, but the fact remains that you KNOW.

My EX did all the lying that he could. He would stand in front of me and deny, deny,deny. I didn't have the proof that could be printed out and all, but I knew. EVERYONE told me. And...even when he was denying all of it, I saw the look on his face - that look of 'oh shit, I am sooooo busted...."

You KNOW.

Do you really need proof to put in front of him? Not really...

Sending you some support...and a big hug...L~

Thanks guys. The only reason I want proof is to get him to leave. He has some serious personality disorder type things going on and can be very unreasonable. I've asked him to leave once in the past and he wouldn't. (This was a long time ago) But we talked so much this summer about what would happen if he had an affair again and how it would be his fault, he would have to be the one to go etc. etc. If I have to leave, I'm not sure I can financially make it and stay in the same city and that will devastate my kids. If he leaves, he can move in with his parents 10 minutes down the road. He does have a weird sense of justice, in the past if I've actually caught him in a lie, he faces the consequences so to speak. So yes, I totally know what's going on and don't need proof for me - I just think it will facilitate the getting rid of the H greatly. And of course, I'm still on the year from now plan, so right now I'm just gathering information, which makes me feel stronger and like I have even the tiniest bit of control in this situation.
Thank you for all the tips btw!!

I used Webwatcher to hide a program on our computer to track the emails between my H and the MOW. You can access it from any other computer.
I live in a no fault state, but we have been married a long time and that goes in my favor as I am a SAHM. My attorney even said that we can subpoena the emails between the two of them from their work computers if needed.
Good luck.