I think you have every right to be upset with your husband. He is married and has no business chatting up women on the internet.
The difference in a fantasy and real life is that a fantasy is something we think about that excites us in some way or another. Sexual fantasies are healthy, but when you obsessively think about them, then it becomes a problem. It sounds as if your husband may be obsessed with them. Does he blow off work or other everday duties in order to chat? Does he snap at you when you question him on the matter?
My other question is 'ringing' means calling other women? If so, then that is a definate PROBLEM because it insinuates that not only is he chatting with these women, he is also calling them and therefor thinking about them through out the day. That is referred to as emotional cheating. Sure, he might be with you physically, but his mind is somewhere else and with somebody else.
Lastly, it seems as though you're not asserting yourself with him. You need to be more assertive. I may be speculating, but it just seems that he is trying to MAKE you believe that what he's doing is perfectly fine and you're the one that is going crazy. That is not acceptable! It alarms me to think that he's trying to manipulate your thoughts in that manner because it shows disrespect and it is most certainly degrading. Why should you feel bad for being mad because he's chatting/talking with other women?! He has no right to make you feel bad for being angry. In my opinion, he should be the one grobbling at your feet asking for forgiveness and not demanding that you be respectful and accept the fact that he chats and talks to other women.
I don't normally advise this to other women, but in this situation, I'm advising that you be angry with him. Show him you're mad and don't back off of it. If he ends up breaking the relationship, then that's on him. He should treat you with the respect you deserve, and what he's doing is extremely disrespectful.
I wish you the best and I hope my advice helped in some way. Other women may have a different take on your situation. My take on it is 'Get mad, and let him know it.' Discuss it further if you'd like. My guess is that he'd only say things like 'I wouldn't chat with these women if you would do......etc.' Given the fact that he has already told you that he thinks he's doing nothing wrong already tells me that he might be the type to try to manipulate you into thinking that you did something wrong. Rest assured, this is NOT your fault, my dear.