Regardless of the type of affair your man is having, the first thing you have to do when your man cheats online is put up your boundaries. You have to know what you will and won't tolerate. You should be prepared to stop being emotionally and physically intimate with him until he stops the affair. If you aren't prepared to kick him out, separtate or breakup, at least speak up and tell him that you are no longer going to be intimate with him until he stops the affair.
Tell him what you don't want in a relationship; "I don't want to be with a someone who has inappropriate conversations online with women"; "I don't want to feel this pain because of a man who goes outside the relationship for validation and intimacy."...
Be calm, direct, soft and honest when you speak with him. Take deep breaths and try as hard as you can to not to get hysterical, be an ice pick or act condescending. Talk to him like he's a friend or a mature child who needs to understand how he has upset you and what you won't accept from him.
Refrain from arguing, blaming, yelling, begging, pleading, making passive aggressive comments and li'l jabs (even if he gets defensive, acts clueless or becomes argumentative). In fact, express your boundaries and try to have no more contact than that. Hold back from engaging him. If he engages you in dialogues or even in loving physical touches, simply tell him again what you don't want in your relationship and if he isn't willing to talk about it or open up, leave the room.
If you have children in the house, remember that being a good parental team is still a must, but you don't have to allow him to use the kids to make you show affection and intimacy to him in their presence. Be kind and polite and keep your children out of it but still stick with your boundaries.
Handling him in this manner allows both of you to cool down and process things. It will show him that you are very upset and are strong enough inside to do something about this problem and not let it continue behind your back. It also shows him that you are mature and know how to handle yourself without getting overly emotional. (Most times strong emotional outbursts or numb cold shoulders keep us 'plugged in' to the drama instead of helping us crawl out of the blackness.)
If he does open up, listen to him and try to be proactive about the health of your relationship. Tell him you want to seek counseling. If he admits that he's wrong (lots of online cheaters claim innocence due to the nature of the connection) and he apologizes, ask him why he does it. Welcome his honesty and try not to guilt-trip him; he may not even know why. If he has been having an emotional affair, ask him what he isn't getting from you that he needs. Refrain from prying or defending yourself. If you feel too emotional, tell him politely that you have to end the conversation for now.
Wait a few days letting things process, and then ask him if he'd like to resume talking about things or would like to go to therapy together. If he says no, remain calm and accept his decline. Refrain from getting angry, pushing him to speak or crying to pull him close to you. Leave him be.