my wife has my daughter and is having a sexual relationship with another man how should I persue this in our divorse
Easy...get a lawyer and ask him. Because you have a child it could get kinda ugly, but if you get yourself a good lawyer and such, tell the judge whats going on, then you could probably get custody of your child, but I'm no law expert or anything, just love the stuff. So your first bet would be to get a lawyer and go over your options with him. I'm sorry about your situation and wish you all the best!
you can not get custody bc she was unfaithful. she would have to be on drugs or a bad mother for you to win custody. adulty will not help you win custody.