Like I said before, save him from himself and yourself in the process. You and I live in the same state, and I know women who have been in your position, and they got half of everything. I don't know if it's state law or if they just had really good attorneys. If you're that worried about it, consult a divorce attorney before you talk to your husband.
At any rate, whether he's having an emotional affair or a physical one, nip this in the bud now. Every dollar he spends on this bovine is less money for your golden years, whether or not they are spent together or apart. Oh, and checking the bills may do you no good. Lots of cheaters get a secret credit card and either manage the account on line or have the statements mailed to a POB. You need to run a credit report on him, which can be done on line for free once a year. If the free one has already been run, then another one can be done for a small fee.
Also I wouldn't worry too much about your friends finding out. If he is indeed spending lots of time with another woman, most, if not all of your friends already know and don't have the nerve to tell you. Stop relying on his honor or guilty conscience to fix this matter. If either of those were motivations for him, he would've ended the affair and/or already come clean. You must protect yourself from both possibilities of acquiring an STD and financial loss against a woman, who at best is a gold digger. If your husbad was being conned in a Nigerian scam you wouldn't hesitate to intervene.
It is important that your husband realize that you are a force to be reckoned with. If your marriage stays together, he will respect you for your strength. If your marriage ends, taking early action will make your life easier later on.