I don't think you should get a divorce over this, but he definitely needs to repent. Something to keep in mind is that men don't look at porn because they want to cheat on their wives. Like a lot of other sinful addictive behaviors, they do it because they enjoy it. There are hormones released and the man gets a little rush from it. Maybe they feel sad or just sort of bored or hurt and want entertainment. Feeling distant or sexually neglected, for example, could make a man more vulnerable to temptation. But usually, it's not really about the wife, and he's not sitting there thinking he's going to do something bad to his wife by watching porn.
On the other hand, I know why you feel like he's cheating on your emotionally by looking with lust, but ultimately it's a sin against God. Chatting with the women could be a manifestation of lust. But if he chats with men, too, it could just be online chatting for entertainment.
He could try to go to some counseling with a Christian counselor or a pastor. A secular counselor probably might not be any good at all for this since porn is so accepted in society. He could also have a male prayer partner or small men's group where he could pray and confess sins to keep him accountable. There are various types of software that block certain websites or report websites he's viewed to accountability partners. He could also just give up internet time or shut off other avenues that he uses to view porn.
Something to keep in mind is even stuff on free TV can entice a man to look with lust. We need to be careful with all forms of media.