Regrets, you really have two choices in front of you.
1. Snoop and get proof of an affair and then confront your husband with that proof. 2. Ignore the affair, focus on DBing, and hope your H's affair fizzles on its own.
What you do is really for you to decide. I decided to snoop, and it was through my W's phone records that I found proof of her affair. Confronting her hasn't done anything to fix our marriage (nor did it make things worse), but it has done a lot to help my mental well being. It also changed the dynamic in my sitch, since my W had been playing the victim until I exposed.
I just couldn't go on pretending like nothing was going on. I needed to know that I wasn't crazy, and I needed to let my W know that her actions were NOT acceptable to me. Exposing the A also forced my W to stop denying what she was doing, and to really own the effects of her terrible behavior. I didn't like seeing my W filled with guilt and shame, but it had to happen. You can't heal from something you're in complete denial about.
If you do decide to snoop, the places that always reveal the most seem to be email and cell phones records. It took me less than 5 minutes of looking at my W's phone bill to know that something was up.
A warning. This isn't for the faint of heart. The things you may find out will be very painful. For me, I'd rather know the truth, no matter how bad it may hurt me.
Regrets,
You asked me to stop by and read your thread, and so I did. I really can't add anything other than what Still Waters has given you here -- in fact, I could have written it myself. However, in reading your emotional state right now, I do NOT think you could handle what gathering some intel ("snooping") would net you, so my advice to you would be Option 2 until you you are stronger.
fwiw, I do think there is someone else. Let me ask you: is that a dealbreaker for you?
