Sex Every Day?
I'm still not over the fact that you have sex every day after six years of marriage. Do you both have a very strong sex drive, or just one of you (I can't tell which one of you it would be from your letter)? It sounds like even though both of you are engaging in sex frequently, you are both in some ways dissatisfied. Maybe start the conversation with him from that perspective.
I may be a little bit naive but I'm not sure what all this on-line business is about.
No Desire to Act on Fantasies
Maybe he feels freer expressing his fantasies on-line which would make sense, since fantasies are usually that and often there is little desire to actually act on them.
You need to talk to him more about this. And maybe to a professional as well.