If you believe she's cheating: don't waste time, energy, & money on searching for proof / evidence. Simply dump the cheater & move on with your life. *** Thats too much drama for me. I don't care to hear the sordid stories... But I'll watch the video with you!!!
Get a private investigator, or just bring it out in the open. If you think she is, go with your gut, talk to a lawyer and serve papers. Tell her you know all about it but dont give any sources and explanations. You dont have to give proof, if you hold out, she will spill the beans on herself. Depends on how hardcore you wanna get. Good Luck