Been there done that. Not a good thing to do cos the result can hurt and more lies come out, and if its a case of her finding out you've done this you've pretty much destroyed the trust that she has in you. i have been in a similar situation. My bf was cheating on me for 7months and if it wasnt for a drunk night alone at his house i would never have checked his logs. Rang him at 2am in the morning cos he was at work said "it was over." Never seen a guy get home so quick from work. Needless to say we've worked it out.
Not the easiest thing to get through, but certainly not the worst. Feel free to send me a private message if you wanna chat.
cass