Sadly, this is an issue I hear all too often and I myself have been in this exact sort of position.
Firstly, you do not mention very much about the background history of your marriage, I can only assume you have been married a while and the throws of passion have maybe simmered some, so that your husband is looking elsewhere for thrills.
Secondly I get from your question that even though your husband chats online, you do not mention the content, or if he has taken it further, and his admittance that he does chat to women, so seems to me that he sees it as harmless fun and nothing to hide. An ego boost or some sense of excitement maybe. Possibly that he is bored in your relationship but possibly isn’t one to go off and leave you or have an affair. To him, the lack of interest in taking it further could be why he is so adamant that it is innocent.
Men can be strange creatures, sometimes child minded and they need attention to thrive. Have you looked at your relationship, the spark and sexiness that once was there. Is it gone? Could he be looking to fill a void that you once filled?
He has maybe grown so accustomed to not having to flirt or show you any real sexy affection, no longer sees it as exciting or necessary, because he married you and you’re there for the keeping. Most men do not realise that they can still flirt and have sexual tension with a spouse, that they really should, and we are all guilty of falling into a neglectful trap.
Sometimes the root of the issue is a lack of openness in your sexual desires and wants. He maybe doesn’t think you will accept some of his preferences and fantasies and it’s easier to play them out with a stranger via the internet than have his wife reject them. So many reasons and possibilities that cause partners to fall into this habit.
If the answer is Yes to any of these, then simply asking him to stop will not be enough. You need to work together to put back that spark, bring back the passion together if you still want a chance at making this work. Relationships are never truly black and white and not always something we should just throw away before evaluating the angles. There are many online sites that are dedicated to bringing the passion back in stale relationships and think you need to sit down together and discuss this with him fully. Possibly look up articles on what he’s doing too and show him that he’s not the first guy to hurt his wife by doing things like this.
He may not see this as cheating because he doesn’t want to admit it to himself, doesn’t want to stop. It feeds a craving and until the root to that craving is sourced then he will carry on.
You need to ask yourself if this could be the case.
On the other hand, some men are just born cheats and liars and will play away from the marital home no matter what. And that is not down to you, but down to the fact they are the ones with commitment issues and you deserve more. In those cases then I would encourage you to walk away, cut loose that someone who clearly does not deserve you.
I really do not get that vibe from the way you phrased this problem. I hope I am accurate in my first response and this is a case of the seven year itch, or the grass is greener and can be rectified in time.
I really do hope that you can get to the heart of this, you seem to be able to communicate with him from your post, and I hope that he is open to talking this through with you and coming to a solution that brings happiness back. Marriage is something we need to constantly work on to keep it working and sometimes we fall off the path and have to find our way back.
Good luck to you, I hope I have been of some help today.