Infidelity Support Group
Any relationship in which one partner engages willfully in sexual relations with another outside of the partnership is considered to have experienced infidelity. This breach of trust is often traumatizing for the faithful partner as well as the relationship, and support is often needed to heal emotionally and to decide whether or not the relationship should continue after...

Hundreds (thousands) of us on this board who have confirmed infidelity will tell you that:
1. They had a gut feeling
2. They wish they had listened to the gut instead of doubting it and trying to talk themselves out of it.
That gut feeling is your subconscious putting together subtle clues and coming to a decision that your conscious mind might now be ready to accept.
Except now you have proof something is going on.
Do not confront or question right now. He will simply lie and hide better. Gather proof if that is what you want.
Fishy as hell.
Listen to your gut. Many of us have and we regretted it.
L~
And if you have access to the phone bill, see how many times her number appears on the bill. That will give you a good idea how much he is really talking with her. If it really is what he is saying, it should only be a few text/calls here and there. Usually if there is more going on than he's let on, you'll see her number frequently everyday. Which if nothing else, would indicate an emotional affair.
Also, if you gain access to his phone and it is a smart phone, which may be harder now, you can install spyware on it that will enable you to track where he's at, record his conversations/text, and allow you to listen in at any point via his microphone.
And if you know where she lives, and it is reasonably close, when he's gone for stated reasons, it wouldn't hurt to drive by her house occasionally to see if his car is there.
But be prepared. You may find out more than you want to know. More details than you want to know. The last thing I expected to find out was my wife was cheating on me, but that's what I discovered, along with some details. I had thought maybe she was involved in some sex chats at most. But I was in for a shocker.