When he started exchanging email and pictures and talking on the phone, that is an indication that he most likely has a potential for actual cheating. His moral compass seems to be quite opposite of yours and the status quo.
He may also be addicted to the Internet and these chat rooms.
You have to decide if you can tolerate this behavior or not. Can you live with this for the rest of your life.
If he has an addiction, and he wants to change, and is willing to work on it, then you and he would need to go to counseling together, and you might attend what is called: co-dependency classes or have yourself evaluated for those tendencies.
(the assumption is that if one is an addict, there must be a co-dependent or enabler in his or her life).
I would start out treating this as it is, unfaithful and secretive behavior; and then open the door to consider that he may actually be addicted to this.
To be sure, the best venue for discussing this with him, may eventually be with a relationship counselor.
Unless he wants to make the changes, you will not get him there and you will not be able to convince him.
YOu have to break this cycle of behavior. Divorce may not be the answer,but neither is allowing him to continue in this behavior.
He is obviously saying, in other words, that he has no intention to change, and he expects you to live with it.,
So you can not change him but you can change yourself. you can not control him, but you can control yourself.
Some people will not change unless they experience a sever emotional event. Such an event could be the fear of losing his wife and children.
I am not telling you to get a divorce or even a separation.
You have a choice to make. If he will not go to counseling, you might go on your own. the counselor will be able to help you explore options. Exploring options in this space is not productive enough, because we lack the personal interaction. You need to be sitting face to face with the counselor to do this.
The big question is: do you want to live the rest of your life like this? If not, then you need to change something, right or wrong, make a move.
Hearts will mend. there is a saying that has truth to it. Time heals all wounds. Absence can give him the time to think and make his own decisions.
Sometimes relieving the stress of the situation can produce great relief for all, including a two year old child.
What ever you do, he has to know you are serious and mean to follow through. Make a decision to act, and stand your ground.