Well, first, Sage, I guess I'd do a little snooping. I know, I know, snooping is frowned upon - but really, if you checked his history and found that he WAS on espn - wouldn't your approach be a little different than if he WAS on hotmail and lied to you about it? (assuming you're not already positive it was hotmail?) Interesting to note that he got so mad but DIDN'T pull up his history to prove to you that you were wrong.
Now, as for him saying divorce - could just be that he's so scared you'll leave him some day because of all this that he'd rather "get it over with" than live in fear? Or could be that he still has something to hide. Obviously it's important to figure out which it is.
So I guess I would approach him with calm, reassuring ("I have forgiven you, I'd never leave you, I just still struggle with trust a little bit, and we need to be able to be completely honest with each other"). Then let him know what concrete things would make you feel better - and ask him what concrete things would make him feel better.
